Refrigeration Manual - HVAC and Refrigeration Information Links

Part IIREFRIGERATION SYSTEM COMPONENTSSection 4. COMPRESSORSReciprocating Compressors.............................. 4-1Open Type Compressors.................................. 4-2Accessible-Hermetic Motor-Compressors........ 4-2Welded Hermetic Motor-Compressors.............. 4-2Compressor Speed........................................... 4-2Basic Compressor Operation............................ 4-4Suction and Discharge Valves.......................... 4-4Compressor Displacement................................ 4-4Clearance Volume............................................. 4-4Lubrication........................................................ 4-5Dry Air Holding Charge..................................... 4-6Compressor Cooling......................................... 4-6Compressor Capacity....................................... 4-6Two Stage Compressors................................... 4-6Compressors with Unloaders .......................... 4-7Tandem Compressors....................................... 4-7Section 5. CONDENSERSAir Cooled Condensers..................................... 5-1Water Cooled Condensers................................ 5-2Evaporative Condensers................................... 5-4Condenser Capacity......................................... 5-5Condensing Temperature.................................. 5-5Non-Condensable Gases.................................. 5-5Condensing Temperature Difference................ 5-6Section 6. EVAPORATORSTypes of Evaporators........................................ 6-1Blower Coil Construction................................... 6-1Pressure Drop and Other Factorsin Evaporator Design................................. 6-2Evaporator Capacity......................................... 6-2Temperature Difference andDehumidification........................................ 6-2Defrosting of Blower Coils................................. 6-3Section 7. CONTROL DEVICES, REFRIGERANTThermostatic Expansion Valves........................ 7- 1Other Types of Expansion Valves..................... 7- 2Distributors........................................................ 7- 2Capillary Tubes................................................. 7- 2Float Valves....................................................... 7- 8Solenoid Valves................................................. 7- 8Crankcase Pressure Regulating Valves............ 7- 9Evaporator Pressure Regulating Valve............. 7- 9Hot Gas Bypass Valves..................................... 7- 9Reversing Valves.............................................. 7-10Check Valves.................................................... 7-10Manual Shut-Off Valves.................................... 7-11Compressor Service Valves.............................. 7-11Schrader Type Valve......................................... 7-11Pressure Relief Valves...................................... 7-12Fusible Plugs.................................................... 7-12Water Regulating Valves................................... 7-12Section 8. CONTROL DEVICES, ELECTRICALControl Differential............................................ 8-1Line Voltage and Low Voltage Controls............ 8-1Low Pressure and High Pressure Controls....... 8-1Condenser Fan Cycling Control........................ 8-2Thermostats...................................................... 8-2Oil Pressure Safety Control.............................. 8-2Time Clocks...................................................... 8-2Relays............................................................... 8-3Time Delay Relay.............................................. 8-3Transformers..................................................... 8-31© 1967 Emerson Climate Technologies, Inc.All rights reserved.

Section 9. MOTORSMotor Temperature............................................ 9-1Open Type Motors and Belt Drives................... 9-1Hermetic Motors................................................ 9-2Nameplate Amperage....................................... 9-2Voltage and Frequency..................................... 9-3Three Phase Motors......................................... 9-3Single Phase Motors......................................... 9-3Split Phase Motors............................................ 9-3Capacitor Start-Induction Run Motors(CSIR)........................................................ 9-4Capacitor Start-Capacitor Run Motors(CSR)......................................................... 9-4Permanent Split Capacitor Motors (PSC)......... 9-5Dual Voltage Motors.......................................... 9-5Two Phase Motors............................................ 9-6Section 10. STARTING EQUIPMENT AND MOTORPROTECTORSContactors and Starters.................................... 10-1Capacitors......................................................... 10-1Start Capacitors................................................ 10-2Run Capacitors................................................. 10-2Reduced Voltage Starting................................. 10-3Motor Protection................................................ 10-8Internal Inherent Line Break Protector.............. 10-8External Inherent Protector............................... 10-9Internal Thermostats......................................... 10-9External Thermostats........................................ 10-9Current Sensitive Protectors............................. 10-9Thermotector..................................................... 10-9Solid State Protectors....................................... 10-9Fuses and Circuit Breakers............................... 10-9Effect of Unbalanced Voltage and Currenton Three Phase Motor Protection.............. 10-10Section 11. ACCESSORIESReceivers.......................................................... 11-1Heat Exchangers.............................................. 11-1Suction Accumulators....................................... 11-1Oil Separators................................................... 11-2Dehydrators...................................................... 11-2Suction Line Filters........................................... 11-2Vibration Eliminators......................................... 11-2Strainers............................................................ 11-3Sight Glass and Moisture Indicators................. 11-3Discharge Mufflers............................................ 11-3Crankcase Heaters........................................... 11-3Refrigeration Gauges........................................ 11-4© 1967 Emerson Climate Technologies, Inc.All rights reserved.

Section 4COMPRESSORSThe compressor has two functions in the compressionrefrigeration cycle. First it removes the refrigerant vaporfrom the evaporator and reduces the pressure in theevaporator to a point where the desired evaporatingtemperature can be maintained. Second, the compressorraises the pressure of the refrigerant vapor to a levelhigh enough so that the saturation temperature is higherthan the temperature of the cooling medium availablefor condensing the refrigerant vapor.There are three basic types of compressors; reciprocating,rotary, and centrifugal. Centrifugal compressors arewidely used in large central air conditioning systems,and rotary compressors are used in the domesticrefrigerator field, but the overwhelming majority ofcompressors used in the smaller horsepower sizesfor commercial, domestic, and industrial applicationsare reciprocating, and this manual will cover onlyreciprocating compressors.RECIPROCATING COMPRESSORSThe design of the reciprocating compressor is somewhatsimilar to a modern automotive engine, with a pistondriven from a crankshaft making alternate suctionand compression strokes in a cylinder equipped withsuction and discharge valves. Since the reciprocatingcompressor is a positive displacement pump, it is suitablefor small displacement volumes, and is quite efficient athigh condensing pressures and high compression ratios.Other advantages are its adaptability to a number ofdifferent refrigerants, the fact that liquid refrigerant maybe easily run through connecting piping because of thehigh pressure created by the compressor, its durability,basic simplicity of design, and relatively low cost.An exploded view of a typical Copelametic® accessiblehermeticmotor-compressor is shown in Figure 10.4-1© 1967 Emerson Climate Technologies, Inc.All rights reserved.

OPEN TYPE COMPRESSORSEarly models of refrigeration compressors were of theso-called open type, with the pistons and cylinders sealedwithin a crankcase, and a crankshaft extending throughthe body for an external power source. A shaft sealaround the crankshaft prevented the loss of refrigerantand oil from the body.Although at one time open type compressors were widelyused, they have many inherent disadvantages such asgreater weight, higher cost, larger size, vulnerability toseal failures, difficult shaft alignment, excessive noise,and short life of belts or direct drive components. Asa result, the open type compressor has been largelyreplaced with the accessible-hermetic and hermetictype motor-compressor in most applications, and theuse of open type compressors continues to declineexcept for specialized applications such as automobileair conditioning.WELDED HERMETIC MOTOR-COMPRESSORSIn an effort to further decrease size and cost, the weldedhermetic motor-compressor has been developed, andis widely used in small horsepower unitary equipment.As in the case of the accessible-hermetic motorcompressoran electric motor is mounted directly on thecompressor crankshaft, but the body is a formed metalshell hermetically sealed by welding. No internal fieldrepairs can be performed on this type of compressorsince the only means of access is by cutting open thecompressor shell.ACCESSIBLE-HERMETIC MOTOR-COMPRESSORSThe accessible-hermetic motor-compressor design waspioneered by Emerson Climate Technologies, Inc. andis widely used in the popular Copelametic® models.The compressor is driven by an electric motor mounteddirectly on the compressor crankshaft, with both the motorand the compressor working parts hermetically sealedwithin a common enclosure. The troublesome shaft sealis eliminated, motors can be sized specifically for theload to be handled, and the resulting design is compact,economical, efficient, and basically maintenance free.Removable heads, stator covers, bottom plates, andhousing covers allow access for easy field repairs inthe event of compressor damage.COMPRESSOR SPEEDEarly models of compressors were designed for relativelyslow speed operation, well below 1,000 RPM. In orderto utilize standard 4 pole electric motors, accessiblehermeticand hermetic motor-compressors introducedoperation at 1,750 RPM (1,450 RPM on 50 cycle). Theincreasing demand for lighter weight and more compactair conditioning equipment has been instrumental in thedevelopment of hermetic motor-compressors equippedwith 2 pole motors operating at 3,500 RPM (2,900 RPMon 50 cycle).Specialized applications such as aircraft, automotive, ormilitary air conditioning equipment utilize even higherspeed compressors, but for the normal commercialand domestic application, the existing 60 cycle electricpower supply will generally limit compressor speeds tothe presently available 1,750 and 3,500 RPM.Higher compressor speeds introduce lubrication andlife problems, and these factors as well as cost, sizeand weight must be considered in compressor designand application.(continued on p. 4-4)© 1967 Emerson Climate Technologies, Inc.All rights reserved.4-2

CROSS-SECTIONAL VIEW OF COPELAMETIC® MOTOR-COMPRESSOR4-3© 1967 Emerson Climate Technologies, Inc.All rights reserved.

BASIC COMPRESSOR OPERATIONA cross-sectional view of a typical Copelametic® motorcompressoris shown in Figure 13. Following is a briefdescription of its operation.As the piston moves downward on the suction stroke,pressure is reduced in the cylinder. When the pressurefalls below that in the compressor suction line, thepressure differential causes the suction valves toopen and forces the refrigerant vapor to flow into thecylinder.As the piston reaches the bottom of its stroke andstarts upward on the compression stroke, pressure isdeveloped in the cylinder, forcing the suction valvesclosed. The pressure in the cylinder continues to riseas the piston moves upward, compressing the vaportrapped in the cylinder. When the pressure in thecylinder exceeds the pressure existing in the compressordischarge line, the discharge valves are forced open,and the compressed gas flows into the discharge lineand on into the condenser.When the piston starts downward, the reduction inpressure allows the discharge valves to close becauseof the higher pressure in the condenser and dischargeline, and the cycle is repeated.For every revolution of the crankshaft, there is both asuction and compression stroke of each piston, so in1,750 RPM motor-compressors there are 1,750 completecompression and suction cycles in each cylinder eachminute, and in 3,500 RPM motor-compressors, 3,500complete cycles each minute.SUCTION AND DISCHARGE VALVESSince the parts of the compressor most apt to requireservice are the suction and discharge valves, onCopelametic® compressors these valves are mountedon a valve plate which can be removed for easy serviceor replacement. A typical valve plate is shown in Figure10, part number 11.Most reciprocating compressor valves are of the reedtype, and must seat properly to avoid leakage. The leastbit of foreign material or corrosion under the valve willcause leakage and the utmost care must be used inprotecting the compressor against contamination.COMPRESSOR DISPLACEMENTThe displacement of a reciprocating compressor is thevolume displaced by the pistons. Emerson ClimateTechnologies, Inc. publishes the displacement of acompressor in terms of cubic feet per hour, but somemanufacturers rate their compressors in terms ofcubic inch displacement per revolution, or in cubic feetper minute. For comparative purposes, compressordisplacement may be calculated by the followingformulas:DisplacementCFM = π x D² x L x RPM x N4 x 1728CFH = π x D² x L x RPM x N x 604 x 1728Cu. In./Rev. = π x D² x L x N4Conversion Factors1750 RPM 3500 RPMCFH = 60 x CFM 60 x CFMCFH = 60.78 x 121.5 xCu. In./Rev. Cu. In./Rev.CFM = 1.013 x 2.025 xCu. In./Rev. Cu. In./Rev.Cu. In./Rev. = .01645 x CFH .00823 x CFHCFM = Cubic feet per minuteCFH = Cubic feet per hourCu. In./Rev. = Cubic inch displacement perrevolutionπ = 3.1416D =Cylinder bore, inchesL =Length of stroke, inchesN =Number of cylindersRPM = Revolutions per minute1728 = Cubic inches per cubic footπD² = Area of a circle4CLEARANCE VOLUMEAs mentioned previously, the volumetric efficiency ofa compressor will vary with compressor design. If thevalves seat properly, the most important factor affectingcompressor efficiency is clearance volume.At the completion of the compression stroke, there stillremains some clearance space which is essential ifthe piston is not to hit the valve plate. There is also agreat deal more space in the discharge valve ports inthe valve plate, since the discharge valves are on top ofthe valve plate. This residual space which is unswept bythe piston at the end of the stroke is termed clearancevolume, and remains filled with hot, compressed gasat the end of the compression stroke.© 1967 Emerson Climate Technologies, Inc.All rights reserved.4-4

When the piston starts down on the suction stroke, theresidual high pressure gas expands and its pressureis reduced. No vapor from the suction line can enterthe cylinder until the pressure in the cylinder has beenreduced below the suction line pressure. Thus, the firstpart of the suction stroke is actually lost from a capacitystandpoint, and as the compression ratio increases, agreater percentage of the suction stroke is occupied bythe residual gas.With high suction pressures, the compression ratio islow and clearance volume is not critical from a capacitystandpoint. Additional clearance volume is also helpfulin reducing the compressor noise level. Since lowergas velocities through the discharge ports reduce bothwear and operating power requirements, on Copeland®brand air conditioning compressors, valve plates aredesigned with greater clearance volume by increasingthe diameter of the discharge ports.On low temperature applications, it is often necessaryto reduce the clearance volume to obtain the desiredcapacity. Low temperature valve plates having smallerdischarge port sizes to reduce the clearance volume areused on low temperature Copelametic® compressors.LUBRICATIONAn adequate supply of oil must be maintained in thecrankcase at all times to insure continuous lubrication.The normal oil level should be maintained at or slightlyabove the center of the sight class.On all Copelametic® compressors 5 H.P. and larger insize, and on 3 H.P. “NR” models, compressor lubricationis provided by means of a positive displacement oilpump. The pump is mounted on the bearing housing,and is driven from a slot in the crankshaft into which theflat end of the oil pump drive shaft is fitted.Oil is forced through a hole in the crankshaft to thecompressor bearings and connecting rods. A springloaded ball check valve serves as a pressure reliefdevice, allowing oil to bypass directly to the compressorcrankcase if the oil pressure rises above its setting.Since the oil pump intake is connected directly to thecompressor crankcase, the oil pump inlet pressurewill always be crankcase pressure, and the oil pumpoutlet pressure will be the sum of crankcase pressureplus oil pump pressure. Therefore, the net oil pumppressure is always the pump outlet pressure minus thecrankcase pressure. When the compressor is operatingwith the suction pressure in a vacuum, the crankcasepressure is negative and must be added to the pumpoutlet pressure to determine the net oil pump pressure.A typical compound gauge is calibrated in inches ofmercury for vacuum readings, and 2 inches of mercuryare approximately equal to 1 psi.For example:Pump Net OilCrankcase Outlet PumpPressure Pressure Pressure50 psig 90 psig 40 psi8” vacuum 36 psig 40 psi(equivalent to a reading of minus 4 psig)In normal operation, the net oil pressure will varydepending on the size of the compressor, the temperatureand viscosity of the oil, and the amount of clearance inthe compressor bearings. Net oil pressures of 30 to 40 psiare normal, but adequate lubrication will be maintainedat pressures down to 10 psi. The bypass valve is setat the factory to prevent the net pump pressure fromexceeding 60 psi.The oil pump may be operated in either direction, thereversing action being accomplished by a friction platewhich shifts the inlet and outlet ports. After prolongedoperation in one direction, wear, corrosion, varnishformation, or burrs may develop on the reversing plate,and this can prevent the pump from reversing. Therefore,on installations where compressors have been inservice for some time, care must be taken to maintainthe original phasing of the motor if for any reason theelectrical connections are disturbed.The presence of liquid refrigerant in the crankcase canmaterially affect the operation of the oil pump. Violentfoaming on start up can result in the loss of oil fromthe crankcase, and a resulting loss of oil pressure untiloil returns to the crankcase. If liquid refrigerant or arefrigerant rich mixture of oil and refrigerant is drawninto the oil pump, the resulting flash gas may resultin large variations and possibly a loss of oil pressure.Crankcase pressure may vary from suction pressuresince liquid refrigerant in the crankcase can pressurizethe crankcase for short intervals, and the oil pressuresafety switch low pressure connection shouldalways be connected to the crankcase.During a rapid pull-down of the refrigerant evaporatingtemperature, the amount of refrigerant in solution in thecrankcase oil will be reduced, and may cause flash gas atthe oil pump. During this period the oil pump must pumpboth the flash gas and oil, and as a result the oil pressuremay decrease temporarily. This will merely cause the oilpump to bypass less oil, and so long as the oil pressureremains above 9 psi, adequate lubrication4-5© 1967 Emerson Climate Technologies, Inc.All rights reserved.

will be maintained. As soon as a stabilized condition isreached, and liquid refrigerant is no longer reaching thepump, the oil pressure will return to normal.DRY AIR HOLDING CHARGEAll Copeland® brand compressors are thoroughlydehydrated at the factory, and are shipped with a dry airholding charge. The pressure inside a factory processedcompressor is a guarantee that the compressor is leaktight, and the interior is absolutely dry. When installed,the compressor must be evacuated to remove the airfrom the system.compressors have been developed for increasedefficiency when evaporating temperatures are in the-30° F. to -80° F. range.Two stage compressors are divided internally into low(or first) and high (or second) stages. On Copelametic®two stage compressors now in production, the ratio oflow stage to high stage displacement is 2 to 1. The threecylinder models have two cylinders on the low stage andone on the high, while the six cylinder models have fourcylinders on the low and two on the high.COMPRESSOR COOLINGAir cooled compressors require an adequate flowof cooling air over the compressor body to preventthe compressor from overheating. The air flow fromthe fan must be discharged directly on the motorcompressor.Air drawn through a compartment in whichthe compressor is located usually will not cool thecompressor adequately.Water cooled compressors are provided with a waterjacket or wrapped with a copper water coil, and watermust be circulated through the cooling circuit when thecompressor is in operation.Refrigerant cooled motor-compressors are designedso that suction gas flows around and through themotor for cooling. At evaporating temperatures below0° F. additional motor cooling by means of air flow isnecessary since the decreasing density of the refrigerantgas reduces its cooling ability.COMPRESSOR CAPACITYCapacity data is available from the manufacturer oneach model of compressor for the refrigerants with whichthe compressor can be used. This data may be in theform of curves or in tabular form, and lists the BTU/hr.capacity at various saturated suction and dischargetemperatures.It is difficult to estimate compressor capacities accuratelyon the basis of displacement and compression ratiobecause of design differences between different models,but occasionally these factors can be valuable inestimating the comparative performance of compressorson the same application.TWO STAGE COMPRESSORSBecause of the high compression ratios encounteredin ultra-low temperature applications, two stageThe suction gas enters the low stage cylinders directlyfrom the suction line, and is discharged into the interstagemanifold at interstage pressure. Since the interstagedischarge vapor has a relatively high temperature,liquid refrigerant must be metered into the interstagemanifold by the desuperheating expansion valve toprovide adequate motor cooling and prevent excessivetemperatures during second stage compression. Thedischarge of the low stage enters the motor chamberand crankcase, so the crankcase is at interstagepressure.Desuperheated refrigerant vapor at interstage pressureenters the suction ports of the high stage cylinders, andis then discharged to the condenser at the condensingpressure.See Figures 6 and 7 on pages 3-6 and 3-7 of Part Ifor typical two stage systems.© 1967 Emerson Climate Technologies, Inc.All rights reserved.4-6

COMPRESSORS WITH UNLOADERSIn order to provide a means of changing compressorcapacity under fluctuating load conditions, largercompressors are frequently equipped with unloaders.Unloaders on reciprocating compressors are of twogeneral types. In the first, suction valves on one or morecylinders are held open by some mechanical means inresponse to a pressure control device. With the suctionvalves open, refrigerant vapor is forced back into thesuction chamber during the compression stroke, andthe cylinder performs no pumping action.A second means of unloading is to bypass a portion ofthe discharge gas into the compressor suction chamber.Care must be taken to avoid excessive dischargetemperatures when this is done.Copelametic® compressors with unloaders have abypass valve so arranged that discharge gas from anunloaded cylinder is returned to the suction chamber.During the unloaded operation, the unloaded cylinderis sealed from the discharge pressure created by theloaded cylinders. Since both suction and dischargepressures on the unloaded cylinder are approximatelythe same, the piston and cylinder do no work otherthan pumping vapor through the bypass circuit, andthe problem of cylinder overheating while unloaded ispractically eliminated. Because of the decreased volumeof suction vapor returning to the compressor from thesystem and available for motor cooling, the operatingrange of unloaded compressors must be restricted,and operation beyond established limits can causecompressor overheating.TANDEM COMPRESSORSIt is often desirable to interconnect two compressors on asingle refrigeration system as a means of varying capacityaccording to the system requirement. This immediatelyintroduces lubrication problems, for unless the pressuresin the two crankcases are equalized, the oil will leavethe crankcase having the highest pressure.In order to solve the troublesome problems of oilequalization and vibration of connecting oil lines whileobtaining the advantage of interconnected compressors,the tandem compressor was developed.Basically this consists of two individual compressorswith an interconnecting housing replacing the individualstator covers. Since each compressor may be operatedindividually, the tandem provides simple, foolproofcapacity reduction with maximum power savings, andgreatly simplifies system control.The tandem offers a much greater factor of safety thana single compressor, and allows staggered starting toreduce inrush current requirements. In the event offailure of one of the compressors, emergency operationof the remaining compressor may be continued untilreplacement of the inoperative motor-compressor. Inorder to provide maximum protection for the system inthe event of the failure of one compressor, a suction linefilter should always be provided in the suction line ofa tandem compressor, and an adequately sized liquidline filter-drier should be provided in the liquid line.4-7© 1967 Emerson Climate Technologies, Inc.All rights reserved.

Section 5CONDENSERSThe condenser is basically a heat exchanger where theheat absorbed by the refrigerant during the evaporatingprocess is given off to the condensing medium. Asmentioned previously, the heat given off by the condenseris always greater than the heat absorbed during theevaporating process because of the heat of compression.As heat is given off by the high temperature highpressure vapor, its temperature falls to the saturationpoint and the vapor condenses to a liquid, hence thename condenser.AIR COOLED CONDENSERSThe most commonly used condenser is of tube andexternal fin construction, which dissipates heat tothe ambient air. Except for very small domestic units,which depend on gravity air circulation, heat transfer isefficiently accomplished by forcing large quantities ofair through a compact condenser assembly. A typicalrefrigeration condensing unit equipped with an air cooledcondenser is shown in Figure 16.surface is amply sized, air cooled condensers can beused satisfactorily in all climatic regions. They have beenused very successfully for many years in hot and dryareas where water is scarce. Because of the increasingscarcity of water in densely populated areas, the useof air cooled condensers will undoubtedly increase inthe future.When space permits, condensers may be made with asingle row of tubing, but in order to achieve compact size,condensers are normally constructed with a relativelysmall face area and several rows of tubing in depth. Asthe air is forced through the condenser, it absorbs heatand the air temperature rises. Therefore, the efficiencyof each succeeding row in the coil decreases, althoughcoils up to eight rows in depth are frequently used.Draw-through fans, which pull the air through thecondenser, result in a more uniform air flow throughthe condenser than the blow-through type. Since evenair distribution will increase the condenser efficiency,draw-through type fans are normally preferred.Most air cooled refrigeration systems which areoperated in low ambient temperatures are susceptibleto damage due to abnormally low head pressure, unlessadequate means of maintaining normal head pressureare provided. This is true, especially with refrigeratedtruck units parked outdoors or in unheated garages, roofmounted refrigeration or air conditioning systems, or anysystem exposed to low outside ambient temperatures.The capacity of refrigerant control devices (expansionvalves, capillary tubes, etc.) is dependent upon thepressure difference across the device. Since they areselected for the desired capacity with normal operatingpressures, abnormally low head pressure reducingthe pressure difference across the expansion valve orcapillary tube, may result in insufficient refrigerant flow.This can cause erratic refrigerant feed to the evaporator,and may result in frosting of the evaporator coil on airconditioning applications. The lower refrigerant velocity,and possibly lower evaporator pressure, permits oil tosettle out and trap in the evaporator, sometimes causingshortage of oil in the compressor crankcase.Air cooled condensers are easy to install, inexpensiveto maintain, require no water, and there is no danger offreezing in cold weather. However, an adequate supplyof fresh air is necessary, and the fan may create noiseproblems in large installations. In very hot regions, therelatively high temperature of the ambient air may resultin high condensing pressures, but if the condenserSeveral proprietary systems are available employingthe principle of partially flooding the condenser withliquid refrigerant to reduce condensing capacity. Someof these systems result in very stable condensingpressures, but usually they require a large increasein the refrigerant charge which may cause problemsin system performance. Controlling the condenser air© 1967 Emerson Climate Technologies, Inc.All rights reserved.5-1

flow by means of louvers is also an effective means ofcondensing pressure control. Cycling the condenser fanis a simple but less effective means of control.WATER COOLED CONDENSERSWhen adequate low cost condensing water is available,water cooled condensers are often desirable becauseof the lower condensing pressures and better headpressure control is possible. Water, particularly fromunderground sources, is frequently much colder thandaytime air temperatures. If evaporative cooling towersare used, the condensing water can be cooled to a pointclosely approaching the ambient wet bulb temperature.This allows the continuous recirculation of condensingwater and reduces water consumption to a minimum.Because of water’s excellent heat transfer characteristics,water cooled condensers can be quite compact. Severaldifferent types of construction are used including shelland coil, shell and tube, and tube within a tube styles.Normally the cooling water is run through tubing or coilswithin a sealed shell into which the hot gas is dischargedfrom the compressor. As the refrigerant condenses itcan be fed out the refrigerant liquid line, thus makingthe use of a separate receiver unnecessary. A watercooled condensing unit equipped with a shell and tubecondenser is shown in Figure 17.A pressure or temperature sensitive modulating watercontrol valve can be used to maintain condensingpressures within the desired range by increasing ordecreasing the rate of water flow as necessary.Cooling water circuits in compressors with water jacketsand in water cooled condensers may be either seriesor parallel as required by the particular application. Theuse of parallel circuits results in a lower pressure dropthrough the circuit, and may be necessary when thetemperature of the cooling water is such that the watertemperature rise must be held to a minimum.Occasionally condensers may be damaged by excessivewater velocities or cavitation on the water side ofthe condenser tubes. In order to prevent operatingdifficulties, care should be taken to follow the installationrecommendations as outlined below:1. Water velocities through the condenser should notexceed 7 feet per second. Higher velocities can resultin “impingement corrosion”. This is a condition in whichprogressive erosion of the tube can occur due to the highwater velocity washing away the inner oxidized surfaceof the tube at points where excessive turbulence mayoccur. This can originate with a minute imperfection onthe tube inner surface, but it becomes progressivelyworse as the pitting increases.(continued on p. 5-4)5-2© 1967 Emerson Climate Technologies, Inc.All rights reserved.

Figure No.18 illustrates the type of circuiting normally used on all standard condensing units using city water supply. All watercooled condensing units are shipped from the factory with the connections as shown above, and water connections must bemodified in the field if parallel circuits are desired.Figure No.19 illustrates a condenser with parallel circuits connected to a motor-compressor with a straight-through circuit. Thistype of circuiting is frequently used when the condensing water is cooled by a water tower . The straight-through compressorcircuit would be used when connecting a motor-compressor wrapped with an external water coil.© 1967 Emerson Climate Technologies, Inc.All rights reserved.5-3

Figure No.20 shows parallel circuits in both water cooled condenser and the motor-compressor water jacket. Each water jacketcircuit is connected in series with one circuit of the split condenser. This type of water circuiting is used when a minimum ofwater pressure drop is required.In order to maintain water velocities at an acceptablelevel, parallel circuiting of the condenser may benecessary when high water flow is required.2. If a water circulating pump is used, install so that thecondenser is fed from the discharge side of the pump. Ifthe pump were on the discharge side of the condenser,the condenser would have a slight vacuum in the watersystem, and therefore the water would be much nearerits boiling point. A combination of a localized hot spot inthe condenser together with a localized velocity increasethat might reduce pressures even lower, could result intriggering a cavitation condition.Cavitation is basically a condition where a fluctuatingcombination of pressure and temperature can causeinstantaneous boiling or flashing of water into vapor, withthe subsequent collapse of the bubbles as the conditionsvary. This can result in very rapid erosion and destructionof the water tube. Maintaining a positive pressure in thecondenser will prevent this condition.3. If the condenser is installed more than 5 feet higherthan the outlet drain point of the condenser, a vacuumbreaker or open vent line should be provided to preventthe discharge line from creating a partial vacuumcondition in the condenser water system. An unventeddischarge connection with a high vertical drop couldresult in cavitation in a manner similar to a pump onthe outlet of the condenser.EVAPORATIVE CONDENSERSEvaporative condensers are frequently used wherelower condensing temperatures are desired than areobtainable with air cooled condensers, and where theavailable water supply may not be adequate for heavywater usage. The hot refrigerant vapor is piped througha spray chamber where it is cooled by evaporation of thewater coming in contact with the refrigerant tubing.Water which is exposed to air flow in a spray chamberwill evaporate rapidly. Latent heat required for theevaporating process is obtained by a reduction in sensibleheat and, therefore, a reduction in the temperature ofthe water remaining. An evaporative spray chambercan reduce the water temperature to a point closelyapproaching the wet bulb temperature of the air.Wet bulb temperature is a term used in air conditioning todescribe the lowest temperature that can be obtained bythe evaporating process. The term wet bulb temperatureis derived from the fact that a common mercury bulbthermometer exposed to the ambient air5-4© 1967 Emerson Climate Technologies, Inc.All rights reserved.

indicates the dry bulb or ambient temperature, while if awick wetted with water is placed around the mercury bulband the thermometer is exposed to rapid air movement,the temperature indicated by the thermometer will be thewet bulb temperature. The difference between the drybulb and wet bulb readings is determined by the rate ofevaporation from the wet surface of the wick, and thisin turn is proportional to the moisture content or vaporpressure of the air. The wet bulb temperature is alwayslower than the dry bulb temperature, and for a given drybulb, the less the moisture content of the air, the lowerthe wet bulb temperature will be.Since the cooling is accomplished by evaporation of thewater, water consumption is only a fraction of that usedin conventional water cooled applications in which thewater once used is discharged to a drain. Evaporativecondensing is therefore widely used in hot, arid regionsof the world.Corrosion, scale formation, and the danger of freezingare problems that must be solved with both evaporativeand water cooled condensers. With both cooling towersand evaporative condensers, a bleed to a drain must beprovided to prevent the concentration of contaminantsin the cooling water.CONDENSER CAPACITYThe heat transfer capacity of a condenser dependsupon several factors:1. Surface area of the condenser .2. Temperature difference between the cooling mediumand the refrigerant gas.3. Velocity of the refrigerant gas in the condenser tubes.Within the normal commercial operating range, thegreater the velocity, the better the heat transfer factor,and the greater the capacity.4. Rate of flow of the cooling medium over or throughthe condenser. Heat transfer increases with velocityfor both air and water, and in the case of air, it alsoincreases with density.5. Material of which the condenser is made. Since heattransfer differs with different materials, more efficientmetals will increase the capacity.6. Cleanliness of the heat transfer surface. Dirt, scale,or corrosion can reduce the heat transfer rate.For a given condenser, the physical characteristicsare fixed, and the primary variable is the temperaturedifference between the refrigerant gas and thecondensing medium.CONDENSING TEMPERATUREThe condensing temperature is the temperature at whichthe refrigerant gas is condensing from a vapor to a liquid.This should not be confused with the temperature ofthe cooling medium, since the condensing temperaturemust always be higher in order for heat transfer to takeplace.In order to condense the refrigerant vapor flowing intothe condenser, heat must flow from the condenser at thesame rate at which heat is introduced by the refrigerantgas entering the condenser. As mentioned previously,the only way in which the capacity of the condensercan be increased under a given set of conditions is byan increase in the temperature difference through thecondenser walls.Since a reciprocating compressor is a positivedisplacement machine, the pressure in the condenserwill continue to increase until such time as thetemperature difference between the cooling medium andthe refrigerant condensing temperature is sufficientlygreat to transfer the necessary amount of heat. Witha large condenser, this temperature difference may bevery small. With a small condenser or in the event airor water flow to the condenser has been blocked, thenecessary temperature difference may be very large.This can result in dangerously high pressures, and it isessential that the condenser is operating properly anytime a refrigeration unit is in operation.The condensing temperature and therefore thecondensing pressure is determined by the capacityof the condenser, the temperature of the coolingmedium, and the heat content of the refrigerant gasbeing discharged from the compressor, which in turn isdetermined by the volume, density and temperature ofthe gas discharged.NON-CONDENSABLE GASESAir is primarily composed of nitrogen and oxygen, andboth elements remain in gaseous form at all temperaturesand pressures encountered in commercial refrigerationand air conditioning systems. Therefore, although thesegases can be liquefied under extremely high pressuresand extremely low temperatures, they may be consideredas non-condensable in a refrigeration system.Scientists have discovered that one of the basic laws ofnature is the fact that in a combination of gases, eachgas exerts its own pressure independently of others,© 1967 Emerson Climate Technologies, Inc.All rights reserved.5-5

and the total pressure existing in a system is the totalof all the gaseous pressures present. A second basiccharacteristic of a gas is that if the space in which it isenclosed remains constant, so that it cannot expand,its pressure will vary directly with the temperature.Therefore, if air is sealed in a system with refrigerant,the nitrogen and oxygen will each add their pressureto the system pressure, and this will increase as thetemperature rises.Since the air is non-condensable, it will usually trapin the top of the condenser and the receiver. Duringoperation the compressor discharge pressure will be acombination of the refrigerant condensing pressure plusthe pressure exerted by the nitrogen and oxygen. Theamount of pressure above normal condensing pressurethat may result will depend on the amount of trapped air,but it can easily reach 40 to 50 psig or more. Any time asystem is running with abnormally high head pressure,air in the system is a prime suspect .CONDENSING TEMPERATURE DIFFERENCEA condenser is normally selected for a system by sizing itto handle the compressor load at a desired temperaturedifference between the condensing temperature andthe expected temperature of the cooling medium.Most air cooled condensers are selected to operate ontemperature differences (commonly called TD) of 20°F. to 30° F. at design conditions, but higher and lowerTDs are sometimes used on specialized applications.Standard production air cooled condensing units areoften designed with one condenser for a wide rangeof applications. In order to cover as wide a range aspossible, the TD at high suction pressures may be from30° F. to 40° F., while at low evaporating temperaturesthe TD often is no more than 4° F. to 10° F. The designcondensing temperature on water cooled units is normallydetermined by the temperature of the water supply andthe water flow rate available, and may vary from 90° F.to 120° F.Since the condenser capacity must be greater than theevaporator capacity by the heat of compression and themotor efficiency loss, the condenser manufacturer mayrate condensers in terms of evaporator capacity, or mayrecommend a factor to allow for the heat of compressionin selecting the proper condenser size.5-6© 1967 Emerson Climate Technologies, Inc.All rights reserved.

Section 6EVAPORATORSThe evaporator is that part of the low pressure side ofthe refrigeration system in which the liquid refrigerantboils or evaporates, absorbing heat as it changes into avapor. It accomplishes the actual purpose of the system,refrigeration.TYPES OF EVAPORATORSIn other types of systems, secondary refrigerants suchas chilled water or brine may be used for the actualspace or product refrigeration while the evaporator is thewater or brine chiller. A complete packaged water chiller,designed to furnish chilled water for air conditioning orother cooling applications is shown in Figure 22.Evaporators are made in many different shapes andstyles to fill specific needs. The most common styleis the blower coil or forced convection evaporator inwhich the refrigerant evaporates inside of finned tubes,extracting heat from air blown through the coil by a fan.However, specific applications may use bare coils withno fins, gravity coils with natural convection air flow,flat plate surface, or other specialized types of heattransfer surface.Direct expansion evaporators are those in which therefrigerant is fed directly into the cooling coil through ametering device such as an expansion valve or capillarytube, absorbing the heat directly through the walls ofthe evaporator from the medium to be cooled. Figure21 shows a direct expansion coil of one manufacturerprior to assembly in a blower unit.BLOWER COIL CONSTRUCTIONA typical blower coil is made up of a direct expansioncoil, mounted in a metal housing complete with a fan forforced air circulation. The coil is normally constructedof copper tubing supported in metal tube sheets, withaluminum fins on the tubing to increase heat transferefficiency.If the evaporator is quite small, there may be only onecontinuous circuit in the coil, but as the size increases,the increasing pressure drop through the longer circuitmakes it necessary to divide the evaporator into severalindividual circuits emptying into a common header. Thevarious circuits are usually fed through a distributor whichequalizes the feed in each circuit in order to maintainhigh evaporator efficiency.The spacing of fins on the refrigerant tubing will varydepending on the application. Low temperature coils mayhave as few as two fins per inch, while air conditioningcoils may have up to twelve per inch or more. In general© 1967 Emerson Climate Technologies, Inc.All rights reserved.6-1

if the evaporator temperature is to be below 32° F. sothat frost will accumulate, fin spacings of 4 per inch orless are commonly used, although closer fin spacingsare sometimes used if efficient defrost systems areavailable. In air conditioning applications, icing of thecoil is seldom a problem, and the limit on fin spacingmay be dictated by the coil’s resistance to air flow.Since the heat transfer efficiency of the coil increaseswith an increase in the mass flow of air passing throughit, high velocities are desirable. However at face velocitiesgreater than 500 to 600 FPM, water collecting on the coilfrom condensation will be blown off into the air stream,and except for specialized applications, these velocitiesare seldom exceeded.PRESSURE DROP AND OTHER FACTORS INEVAPORATOR DESIGNAs mentioned previously, pressure drop occurring in theevaporator results in a loss of system capacity due tothe lower pressure at the outlet of the evaporator coil.With a reduction in suction pressure, the specific volumeof the gas returning to the compressor increases, andthe weight of the refrigerant pumped by the compressordecreases.However there are other factors which must also beconsidered in evaporator design. If the evaporator tubingis too large, refrigerant gas velocities may become solow that oil will accumulate in the tubing and will not bereturned to the compressor. The only means of assuringsatisfactory oil circulation is by maintaining adequate gasvelocities. The heat transfer ability of the tubing may alsobe greatly decreased if velocities are not sufficient toscrub the interior tubing wall, and keep it clear of an oilfilm. The goals of low pressure drop and high velocitiesare directly opposed, so the final evaporator design mustbe a compromise.Pressure drops through the evaporator of approximately1 to 2 psi are acceptable on most medium and hightemperature applications, and 1/2 to 1 psi are commonin low temperature evaporators.EVAPORATOR CAPACITYThe factors affecting evaporator capacity are quite similarto those affecting condenser capacity.1. Surface area or size of the evaporator .2. Temperature difference between the evaporatingrefrigerant and the medium being cooled.3. Velocity of gas in the evaporator tubes. In the normalcommercial range, the higher the velocity the greaterthe heat transfer rate.4. The velocity and rate of flow over the evaporatorsurface of the medium being cooled.5. Material used in evaporator construction.6. The bond between the fins and tubing is quiteimportant. Without a tight bond, heat transfer will begreatly decreased.7. Accumulation of frost on evaporator fins. Operationat temperatures below freezing with blower coils willcause the formation of ice and frost on the tubesand fins. This can both reduce the air flow over theevaporator and reduce the heat transfer rate.8. Type of medium to be cooled. Heat flows almost fivetimes more effectively from a liquid to the evaporatorthan from air .9. Dewpoint of the entering air. If the evaporatortemperature is below the dewpoint of the enteringair, latent as well as sensible cooling will occur.TEMPERATURE DIFFERENCE ANDDEHUMIDIFICATIONSince for a given installation, the physical characteristicsare fixed, the primary variable as in the case of thecondenser, is the temperature difference between theevaporating refrigerant and the medium being cooled,commonly called the TD. For a blower coil, the colderthe refrigerant with respect to the temperature of the airentering the evaporator, the greater will be the capacityof the coil.Temperature differences of 5° F. to 20° F. are commonlyused. Usually for best economy, the TD should be keptas low as possible, since operation of the compressorwill be more efficient at higher suction pressures.The amount of moisture condensed out of the air isin direct relation to the temperature of the coil, and acoil operating with too great a differential between theevaporating temperature and the entering air temperaturewill tend to produce a low humidity condition in therefrigerated space. In the storage of leafy vegetables,meats, fruits, and other similar perishable items, lowhumidity will result in excessive dehydration and damageto the product. For perishable commodities requiring avery high relative humidity (approximately 90%) a TDfrom 8° F. to 12° F. is recommended, and for relativehumidities slightly lower (approximately 80%) a TD from12° F. to 16° F. is normally adequate.6-2© 1967 Emerson Climate Technologies, Inc.All rights reserved.

DEFROSTING OF BLOWER COILSIce and frost will accumulate continuously on coilsoperating below freezing temperatures, and air flowthrough the coil will be eventually blocked unless thefrost is removed. To allow continuous operation onrefrigeration applications where frost accumulation canoccur, periodic defrost cycles are necessary.If the air returning to the evaporator is well above 32°F., defrosting can be accomplished by allowing thefan to continue operation while the compressor is shutdown, either for a preset time period or until the coiltemperature rises a few degrees above 32° F., themelting temperature of the frost.For low temperature applications, some source of heatmust be supplied to melt the ice. Electric defrost systemsutilize electric heater coils or rods in the evaporator.Proprietary systems using water for defrosting areavailable. Hot gas defrosting is widely used, with thedischarge gas from the compressor bypassing thecondenser and discharging directly into the evaporatorinlet. In hot gas defrost systems, the heat of compressionor some source of stored heat provides defrost heat,and adequate protective devices such as re-evaporatorsor suction accumulators must be provided if necessaryto prevent liquid refrigerant from returning to thecompressor. Other systems may utilize reverse cycledefrosting, in which the flow of refrigerant is reversedto convert the evaporator temporarily into a condenseruntil the defrost period is complete.To prevent refreezing of the melted condensate in theevaporator drain pan, a drain pan heater is required onlow temperature systems.© 1967 Emerson Climate Technologies, Inc.All rights reserved.6-3

In modern refrigeration practice, a wide variety ofrefrigerant control devices are used to obtain efficienteconomic operation. Small systems with manual controlor simple “on-off” automatic control may require only oneor two controls, but large systems with more elaborateautomatic control may have a multitude of controls,the proper operation of each being essential to thesatisfactory performance of the system.In order to adjust a control for efficient performance,or recognize the effect of a malfunction, it is essentialthat the function, operation, and application of eachrefrigeration control be completely understood.THERMOSTATIC EXPANSION VALVESThe most commonly used device for controlling the flowof liquid refrigerant into the evaporator is the thermostaticexpansion valve. An orifice in the valve meters the flowinto the evaporator, the rate of flow being modulatedas required by a needle type plunger and seat, whichvaries the orifice opening.Section 7CONTROL DEVICES, REFRIGERANTThe needle is controlled by a diaphragm subject to threeforces. The evaporator pressure is exerted beneath thediaphragm tending to close the valve. The force of asuperheat spring is also exerted beneath the diaphragmin the closing direction. Opposing these two forces isthe pressure exerted by the charge in the thermal bulb,which is attached to the suction line at the outlet of theevaporator.It is most convenient to visualize the action of thethermostatic expansion valve by considering thethermal bulb charge to be the same refrigerant as thatbeing used in the system. With the unit in operation,the refrigerant in the evaporator is evaporating at itssaturation temperature and pressure. So long as thethermal bulb is exposed to a higher temperature itwill exert a higher pressure than the refrigerant in theevaporator, and therefore the net effect of these twopressures is to open the valve. The superheat springpressure is a fixed pressure causing the valve to closewhenever the net difference between the bulb pressureand the evaporator pressure is less than the superheatspring setting.As the temperature of the refrigerant gas leaving theevaporator rises (an increase in superheat) the pressureexerted by the thermal bulb at the outlet of the coilincreases, and the expansion valve flow increases; asthe temperature of the leaving gas decreases (a decreasein superheat) the pressure exerted by the thermal bulbdecreases, and the expansion valve closes slightly andthe flow decreases.With an evaporator and an expansion valve correctlysized for the load, the expansion valve feed will be quitestable at the desired superheat setting. An oversizedexpansion valve or an oversized evaporator can causeerratic feeding of the evaporator, which may result inlarge fluctuations in compressor suction pressure, andpossible liquid return to the compressor.Because of the pressure drop due to refrigerant flowthrough the evaporator, the evaporating pressure at theoutlet of the evaporator coil will be lower than that at theexpansion valve. If this pressure drop is of any magnitude,a higher superheat will be required to bring the forcesacting on the valve diaphragm into equilibrium, andthe evaporator will be partially starved. To compensatefor pressure drop through the evaporator, an externalequalizer connection is often used on the expansionvalve. This introduces the evaporator outlet pressureunder the valve diaphragm, rather than the evaporatorinlet pressure, and the valve operation is then free fromany influence due to evaporator pressure drop. Valveswith external equalizer connections are recommendedwhenever the pressure drop through the evaporator7-1© 1967 Emerson Climate Technologies, Inc.All rights reserved.

is above 2 1/2 psi for high temperature applications,1 1/2 psi in the medium temperature range, and 1/2psi in the low temperature range. Valves with externalequalizers must be employed when a pressure droptype of distributor is used.Pressure limiting expansion valves are often used to limitthe power requirement of the compressor. The valve isconstructed in such a manner that it limits the suctionpressure to a given maximum value, and restricts therefrigerant feed if the suction pressure rises above thatpoint.Gas charged pressure limiting valves have a limitedcharge, and at temperatures of the thermal bulbequivalent to its maximum operating pressure, all of theliquid charge has vaporized, and any further increasein temperature can only superheat the gas, but cannotexert additional pressure. Any increase in evaporatorpressure will then act as a closing force on the expansionvalve. The disadvantage of the gas charged valve is thepossibility of the limited charge condensing in the headof the expansion valve, if the head is colder than thethermal bulb, causing the valve to lose control of theliquid feed. With gas charged valves, the thermal bulbmust always be colder than the head of the valve, andthe gas charged valve normally is used only on hightemperature applications such as air conditioning.Mechanical limiting valves are available, usually witha spring loaded double diaphragm type construction.If the evaporator reaches a preset pressure, thediaphragm collapses, and the valve feed is restricteduntil the pressure decreases sufficiently for the springtension to restore the diaphragm to its normal operatingposition.In order to achieve closer control for varying applications,expansion valves are available with different typesof charge in the thermal bulb, each having differentoperating characteristics. The superheat spring is alsonormally equipped with an external adjusting screw sothat it can be set for the desired superheat on a givenapplication. Before adjusting any expansion valve, theexact characteristics of the valve should be thoroughlyunderstood. The manufacturer’s catalog data must beconsulted for detailed information on a given valve.OTHER TYPES OF EXPANSION VALVESThe automatic expansion valve is really better describedas a constant pressure expansion valve, since itmodulates its feed to maintain a constant preset pressurein the evaporator. The automatic expansion valve waswidely used at one time, but because of its tendencyto starve the evaporator on heavy loads, and flood theevaporator on light loads, it has been largely replaced bythe thermostatic expansion valve and capillary tubes.Hand expansion valves are sometimes used when anoperator is available and manual liquid refrigerant feedis acceptable. A needle valve is adjusted as required tomaintain the desired flow.DISTRIBUTORSWhen the refrigeration load is such that large evaporatorsare required, multiple refrigerant circuits are necessaryto avoid excessive pressure drop through the evaporator.To insure uniform feed from the expansion valve to eachof the various circuits, a refrigerant distributor is normallyused. A typical distributor mounted on a direct expansioncoil is shown in Figure 21, page 6-1.As liquid refrigerant is fed through the expansion valve,a portion of the liquid flashes into vapor in order toreduce the liquid temperature to evaporator temperature.This combination of liquid and flash gas is fed intothe distributor from the expansion valve, and is thendistributed evenly through small feeder tubes, the numberdepending on the construction of the distributor and thenumber of circuits required to provide proper refrigerantvelocity in the evaporator .Without the distributor, the flow would separate intoseparate gas and liquid layers, resulting in the starvingof some evaporator circuits. To avoid variations in circuitfeed, extreme care must be taken to insure that tubinglengths are equal, so equal resistance is offered byeach circuit.There are two different approaches in the design of adistributor. A high-pressure drop distributor dependson the turbulence created by an orifice to achievegood distribution. A low-pressure drop distributordepends on a contour flow pattern with high velocity inthe distributor throat to give proper distribution of therefrigerant flow. Both types of distributor give satisfactoryperformance when properly applied in accordance withthe manufacturer’s instructions.CAPILLARY TUBESOn small unitary equipment such as package airconditioners, domestic refrigeration equipment, andself-contained commercial refrigeration cases, capillarytubes are widely used for liquid refrigerant control. Acapillary tube is a length of tubing of small diameter withthe internal diameter held to extremely close tolerances.It is used as a fixed orifice to perform the same function(continued on p. 7-8)© 1967 Emerson Climate Technologies, Inc.All rights reserved.7-2

CAPILLARY TUBE SELECTION R-22HIGH TEMPERATURE45° F. evaporating temperature (Preliminary Selection Only)Final Selection Should Be Determined by Unit Test**Length to balance unit at 45° F. evaporating,130° F. condensing, 10° F.Sub-cooling.7-3© 1967 Emerson Climate Technologies, Inc.All rights reserved.

CAPILLARY TUBE SELECTION R-22MEDIUM TEMPERATURE25°F, to 10°F. Evaporating Temperature (Preliminary Selection Only)Selection Should Be Determined by Unit Test**Length to balance unit with 115°F. condensing, °F. sub-cooling incondenser, Heat Exchanger to give 15°F. sub-cooling.© 1967 Emerson Climate Technologies, Inc.All rights reserved.7-4

CAPILLARY TUBE SELECTION R-12MEDIUM TEMPERATURE25°F, to 10°F. Evaporating Temperature (Preliminary Selection Only)Final Selection Should Be Determined by Unit Test**Length to balance unit with 115°F. condensing, 5°F.sub-cooling in condenser, Heat Exchanger to give 15°F.sub-cooling.7-5© 1967 Emerson Climate Technologies, Inc.All rights reserved.

CAPILLARY TUBE SELECTION R-22LOW TEMPERATURE15°F. to 25°F. Evaporating Temperature(Preliminary Selection Only)Final Selection Should Be Determined by Unit Test*Length to balance unit at 110°F. condensing and 20°F.Liquid sub-cooling (15°F. in condenser, 15°F in heatexchanger)© 1967 Emerson Climate Technologies, Inc.All rights reserved.7-6

CAPILLARY TUBE SELECTION R-502LOW TEMPERATURE15°F. to 25°F. Evaporating Temperature(Preliminary Selection Only)Final Selection Should Be Determined by Unit Test*Length to balance unit at 110°F. condensing and 20°F.Liquid sub-cooling (15°F. in condenser, 15°F in heatexchanger)7-7© 1967 Emerson Climate Technologies, Inc.All rights reserved.

as the expansion valve, to separate the high and lowpressure sides of the system, and meter the proper feedof liquid refrigerant.Since there are no moving parts, it is simple and troublefree if kept free of foreign material. A capillary tube is ofvery small diameter, and absolute freedom from foreignmatter and moisture is essential, making a factory sealedunit a practical necessity.Since the orifice is fixed, the rate of feed is relativelyinflexible. Under conditions of constant load, and constantdischarge and suction pressures, the capillary tubeperforms very satisfactorily. However, changes in theevaporator load or fluctuations in head pressure canresult in under or over feeding of the evaporator.A major advantage of the capillary tube in some systemsis the fact that refrigerant continues to flow into theevaporator after the compressor stops operation, thusequalizing pressures on the high and low sides ofthe system. This allows the use of low starting torquemotors.The refrigerant charge is critical in capillary tubesystems since normally there is no receiver to storeexcess refrigerant. Too much refrigerant will causehigh discharge pressures and motor overloading, andpossible liquid floodback to the compressor during theoff cycle; too little will allow vapor to enter the capillarytube causing a loss in system capacity.to maintain a given liquid level. Such applications arequite specialized and the manufacturer’s instructionsshould be followed closely. Unless some means isprovided for positive oil return, oil may accumulate in afloat chamber causing lubrication difficulties.Commercial or domestic applications using either highside or low side float chambers for liquid feed havebeen largely replaced by capillary tube and expansionvalve control.SOLENOID VALVESA solenoid valve is an electrically controlled refrigerantflow control valve. It is not a modulating valve, and iseither open or closed.The valve consists of a body, a plunger with an ironcore which seats in the valve orifice, and an electricalsolenoid coil. A normally closed solenoid valve is closedwhen the coil is deenergized and the plunger is seated.When the solenoid coil is energized, the magnetic effectof the coil lifts the plunger and opens the valve. Normallyopen valves with a reverse type action are made, butare rarely used.Solenoid valves are commonly used in refrigerantliquid and hot gas lines to stop refrigerant flow whennot desired, or to isolate individual evaporators whenDue to its basic simplicity, the elimination of the need fora receiver, and the low starting torque requirement, acapillary tube system is the least expensive of all liquidcontrol systems.Sizing of a capillary tube is difficult to calculate accurately,and can best be determined by actual test on the system.Once determined, the proper size capillary tube canbe applied to identical systems, so it is well adapted toproduction units. Figures 24, 25, 26, 27, and 28 givetentative selection data for capillary tubes.FLOAT VALVESOn some specialized applications, it may be desirableto operate with completely flooded systems, that is, withthe evaporator completely filled with liquid refrigerant. Atypical application might be an industrial process coolinginstallation where a brine or liquid is piped through a chillershell in which the refrigerant level is to be maintained.Special liquid level controls are available from expansionvalve manufacturers. These normally are mounted in asecondary float chamber and modulate flow as necessary© 1967 Emerson Climate Technologies, Inc.All rights reserved.7-8

multiple evaporators are used. On large installations,large numbers of solenoid valves may be necessary forsatisfactory automatic control.similarly to the crankcase pressure regulator, except thatit is responsive to inlet pressure. It should be located inthe suction line at the evaporator outlet.CRANKCASE PRESSURE REGULATING VALVESThis type of valve, commonly called a CPR valve ora holdback valve, limits the suction pressure at thecompressor below a preset limit to prevent overloadingof the compressor motor. The valve setting is determinedby a pressure spring, and the valve modulates fromfully open to fully closed in response to outlet pressure,closing on a rise in outlet pressure.The crankcase pressure regulating valve should belocated in the suction line between the evaporator andthe compressor. Since the power requirement of thecompressor declines with a fall in suction pressure, theCPR valve is normally used to prevent motor overloadingon low temperature units during pulldown or defrostcycles. Use of the valve permits the application of aAn EPR valve modulates from fully open to fully closed,closing on a fall in inlet pressure, and its sole function isto prevent the evaporator pressure from falling below apredetermined value for which the regulator has beenset.HOT GAS BYPASS VALVESHot gas bypass valves are used where it is desirableto modulate the compressor capacity and at the sametime prevent the suction pressure from falling toobjectionable low levels. These valves operate in thelarger displacement compressor without overloading agiven size motor, but pressure drop through the valvemay result in an unacceptable loss of system capacityunless the valve is adequately sized.EVAPORATOR PRESSURE REGULATING VALVEOn systems with multiple evaporators operating atdifferent temperatures, or on systems where theevaporating temperature cannot be allowed to fall belowa given temperature, an evaporator pressure regulatorvalve is frequently used to control the evaporatingtemperature. This valve, often called an EPR valve, acts7-9© 1967 Emerson Climate Technologies, Inc.All rights reserved.

same fashion as crankcase pressure regulators sincethey are responsive to outlet pressure, modulate fromfully open to fully closed, and open in response to adecrease in downstream pressure. The constructionmust be suitable to withstand the high temperaturedischarge gas from the compressor.Hot gas valves are set to maintain a desired minimumpressure by spring tension, and may be either director pilot operated. They are normally equipped with anexternal equalizer connection, which operates in thesame fashion as an external equalizer on an expansionvalve to compensate for pressure drops in the lines. Theexternal equalizer should be attached to the suction lineat the point where it is desired to control the suctionpressure.REVERSING VALVESIn recent years, usage of the “heat pump” principle toenable an air conditioning unit to supply both cooling andheating has become increasingly popular. Basically thisinvolves switching the functions of the evaporator andcondenser by a change in refrigerant flow as desired, sothat the indoor coil becomes the evaporator for coolingpurposes, and the condenser for heating usage. Theoutdoor coil in turn is a condenser during the coolingcycle, and an evaporator during the heating cycle.To conveniently reverse the system operation, four-wayreversing valves have been developed. By means ofa slide action actuated by a solenoid, the connectionsfrom the compressor suction and discharge ports to theevaporator and condenser can be reversed at will.Three-way valves are being increasingly used for hotgas defrosting. This valve enables the flow of hot gasfrom the compressor discharge valve to be shunted fromthe condenser to the evaporator for defrosting purposes,and then conveniently returned to the condenser whennormal cooling is resumed.CHECK VALVESIt is often desirable to prevent refrigerant from reversingits direction of flow during an off cycle, or during achange in the operating cycle. A simple spring loadedvalve such as shown in Figure 34 allows flow in onedirection only, and closes if pressures are such thatreverse flow could occur. Check valves may be usedin either liquid or gas lines, and are frequently used toprevent backflow of liquid refrigerant or hot gas in lowambient condenser controls, and in reverse cycle heatpumps. Check valves used in refrigeration systemsshould be spring loaded to prevent noise and chattering© 1967 Emerson Climate Technologies, Inc.All rights reserved.7-10

which may be caused by pulsations in refrigerant floworiginating in the compressor.MANUAL SHUT-OFF VALVESManual shut-off valves are often used so that portionsof the refrigeration system can be isolated for service orrepairs. Special valves designed for refrigeration usageare required to avoid leakage.COMPRESSOR SERVICE VALVESCompressor suction and discharge service valves areshut-off valves with a manual operated stem. Mostservice valves are equipped with a gauge port so thatthe refrigerant operating pressure may be observed.When the valve is back-seated (the stem turned all theway out) the gauge port is closed and the valve is open.If the valve is front-seated (the stem turned all the wayin) the gauge port is open to the compressor and theline connection is closed. In order to read the pressurewhile the compressor is in operation, the valve shouldbe back-seated, and then turned in one or two turnsin order to slightly open the connection to the gaugeport. The compressor is always open to either the lineor the gauge port, or both if the valve is neither frontnor back-seated.SCHRADER TYPE VALVEThe Schrader type valve is a recent developmentfor convenient checking of system pressures whereit is not economical, convenient, or possible to usethe compressor service valves with gauge ports. TheSchrader type valve is similar in appearance andprinciple to the air valve used on automobile or bicycletires, and must have a cap for the fitting to insure leakproofoperation.7-11© 1967 Emerson Climate Technologies, Inc.All rights reserved.

This type of valve enables checking of the systempressure, or charging refrigerant without disturbingthe unit operation. An adaptor is necessary for thestandard serviceman’s gauge or hose connection to fitthe Schrader type valve.PRESSURE RELIEF VALVESSafety relief valves are required by many localconstruction codes. Various types of relief valves areavailable, and the system requirement may be dictated bythe local code requirement. Normally code requirementsspecify that the ultimate strength of the high side partsshall be a minimum of 5 times the discharge or rupturepressure of the relief valve, and that all condensing unitswith pressure vessels exceeding 3 cubic feet intervalvolume shall be protected by a pressure relief device.Discharge may be to the atmosphere, or it may be adischarge from the high pressure side of the system tothe low pressure side.A typical reseating type valve is shown in Figure 38.The valve opens at a preset pressure, and refrigerantis discharged until the pressure falls to the reseatingpoint.Some Copeland® brand compressors have reseatingtype pressure relief valves installed internally in thedischarge chamber which allow excessive pressuresto discharge to the suction chamber. A typical internaltype valve is shown in Figure 39.Rupture disc type relief devices have a thin disc which isdesigned to rupture at a given relief pressure, dischargingthe refrigerant to the atmosphere.FUSIBLE PLUGSA fusible plug is a safety device with a metal inserthaving a specified melting point. The allowable meltingpoint is defined by code, but normally it is the saturationtemperature of the refrigerant at a pressure no greaterthan 40% of the ultimate bursting pressure of therefrigerant containing vessel, or the critical temperatureof the refrigerant, whichever is lower .Fusible plugs are limited to units with pressure vesselsnot exceeding 3 cubic feet internal gross volume. Theyare used as a safety device in the event of fire, areresponsive to temperature only and will not protectagainst excessively high pressures.© 1967 Emerson Climate Technologies, Inc.All rights reserved.7-12

WATER REGULATING VALVESOn water cooled condensers, a modulating waterregulating valve is normally used to economize onwater usage and to control condensing pressureswithin reasonable limits. Water valves may be eitherpressure or temperature actuated and act to throttleflow as necessary.7-13© 1967 Emerson Climate Technologies, Inc.All rights reserved.

Section 8CONTROL DEVICES, ELECTRICALBoth electrical and pneumatic controls are widely usedfor air conditioning and refrigeration system control.Pneumatic controls are primarily used on large centralsystems, while electric controls are used on applicationsof all sizes. Since electric controls are used almostexclusively in the commercial refrigeration field, thismanual will cover only electric controls.CONTROL DIFFERENTIALThe basic function of most electrical control devices isto make or break an electric circuit which in turn controlsa contactor, a solenoid coil, or some other functioningpart of the system. Controls are available which maymake or break a circuit on either a rise or fall in pressureor temperature. The type of action required dependson the function of the control and the medium beingcontrolled.voltage to the control circuit voltage, usually 24 volts.LOW PRESSURE AND HIGH PRESSURECONTROLSA low pressure control is actuated by the refrigerantsuction pressure, and normally is used to cycle thecompressor for capacity control purposes, or as a lowlimit control. The low pressure control often is used asthe only control on small systems which can toleratesome fluctuations in the temperature to be maintained.The standard low pressure control makes on a rise inpressure, and breaks on a fall in pressure.The point at which a control closes a contact and makesa circuit is called the cut-in point. The point at which thecontrol opens the switch and breaks the circuit is calledthe cut-out point. The difference between the cut-in andcut-out points is known as the differential.A very small differential maintains close control butcan cause short cycling of the compressor. A largedifferential will give a longer running cycle, but mayresult in fluctuations in the pressure or temperaturebeing controlled, so the final operating differential mustbe a compromise.The differential may be either fixed or adjustable,depending on the construction of the control. Adjustmentof controls varies depending on the type and themanufacturer. On some controls, both the cut-in andcut-out points may be set at the desired points. On manypressure controls, the differential can be adjusted, andthis in turn may affect either the cut-in or the cut-outpoint.LINE VOLTAGE AND LOW VOLTAGE CONTROLSLine voltage controls are designed to operate on thesame voltage as that supplied to the compressor. Both110 and 220 volt controls are quite commonly used,and 440 volt controls are available but are seldomused due to the danger from high voltage at the wiringconnections.Local codes often require low voltage controls, and acontrol circuit transformer may be used to reduce lineA high pressure control senses the compressordischarge pressure, and is normally used to stop thecompressor in case of excessively high pressures.Since the allowable pressure limit varies with differentrefrigerants, the proper high pressure control for therefrigerant in the system must be used. A high pressurecontrol makes on a fall in pressure and breaks on arise in pressure. Either manual reset or automatic resetcontrols are available, the choice depending on thedesired system operation.Dual pressure controls are comprised of a low pressureand a high pressure control mounted in a single housingwith a single switch operated by either control.© 1967 Emerson Climate Technologies, Inc.All rights reserved.8-1

CONDENSER FAN CYCLING CONTROLIn order to maintain air cooled condensing pressuresat a satisfactory level during low ambient conditions,a condenser fan pressure control is frequently used.The control acts to break the circuit to the condenserfan on a drop in condensing pressure and makes thecircuit on a rise in condensing pressure. Since this isthe reverse of the action on a normal high pressurecontrol, this is often described as a reverse acting highpressure control.THERMOSTATSA thermostat acts to make or break a circuit in responseto a change in temperature. There are numerous typesof thermostats ranging from a simple bimetallic switch tomultiple switch controls operating from remote sensingbulbs. Thermostats may have a fixed control point ormay have variable adjustments.Normally a cooling thermostat will make on a rise intemperature and break on a fall in temperature, whilea heating thermostat will make on a fall in temperatureand break on a rise.OIL PRESSURE SAFETY CONTROLSpecial pressure controls have been developed toprotect the compressor against loss of oil pressure. Thecontrol is actuated by the difference in pressure betweenthe outlet oil pressure of the oil pump and crankcasepressure. Since the inlet pressure of the oil pump isalways crankcase pressure, the net difference in thetwo pressures is the net lubrication oil pressure.Oil pressure safety controls are available with bothadjustable and non-adjustable control settings, but thenon-adjustable type is preferred to avoid difficultiesarising from improper field adjustment.If the oil pressure falls below safe limits, the controlbreaks to stop the compressor. As an added refinement,a time delay circuit is incorporated to delay the actionof the control for a period up to 2 minutes to allow thecompressor to establish oil pressure on start-up withoutnuisance tripping.TIME CLOCKSFrequently it is desirable to stop the compressoroperation for a period of time to allow defrosting. In orderto insure that this is done regularly at convenient times,a time clock can be used to either make or break wiringcircuits at preset time intervals. Clocks are available forboth 24 hour and 7 day cycles, and the defrost intervaland time of initiation and termination can be adjustedas desired.Various types of defrost control circuits are commonlyused, such as time initiated, time terminated; timeinitiated, temperature terminated; or time initiated,pressure terminated. Normally on circuits with pressure ortemperature termination, an overriding time termination is8-2© 1967 Emerson Climate Technologies, Inc.All rights reserved.

provided in the event the defrost cycle for some reasonis abnormally prolonged.RELAYSA relay consists of a set of contacts together with amagnetic coil mechanism which controls the contactposition. The contacts may be normally open or normallyclosed when not energized, and a given relay may havefrom 1 to 5 or more sets of contacts. When the coil isenergized, the contacts reverse their action and makeor break various circuits as desired.A relay may be used to control a large amperage load bymeans of a pilot circuit, to allow interlocking of controlson separate circuits, or for any application where remotecontrol is required.Most relays are of the potential type, and are actuatedwhen the coil is energized with the proper voltage.Current relays are actuated by a sufficient currentflowing through the relay coil, and are normally usedwhen it is desirable to make or break a circuit when alarge change in current flow occurs. These are used insingle phase motor starting circuits, and occasionallyin safety circuits.An impedance relay is similar to a normal potential relayexcept that the coil is wound so as to create a highresistance to current passage. When wired in parallelwith a normal relay, the high impedance (resistance)of the relay will shunt the current to the normal circuitand the impedance coil will be inoperative. If the normalcircuit is opened and the current must pass through theimpedance relay, the relay coil will be energized and theimpedance relay will operate. The voltage drop across therelay coil is so large that other magnetic coils in serieswith the impedance coil will not operate because of theresulting low voltage. Impedance relays are frequentlyused for safety lock-out circuits in the event of a motorprotector trip.TIME DELAY RELAYSome relays are constructed with a time delay actionso that the relay must be energized for a predeterminedlength of time before the magnetic coil can actuate thecontacts. The time delay is normally non-adjustable, butrelays are available with varying periods of delay.This type of relay may be required for part winding startmotors; in circuits to prevent short cycling, or for otherspecialized applications.TRANSFORMERSA transformer is an electrical device for transferringelectrical energy from one circuit to another at adifferent voltage by means of electromagnetic induction.Transformers are frequently used in control circuits tostep voltage down from line voltage to a lower controlcircuit voltage. There are no moving parts and the actionof the transformer is determined by its coil windings.The transformer output is limited by its size, buttransformers are available for almost any output desiredfrom a tiny alarm bell circuit to the giant transformersused on high voltage power transmission lines.The selection of control circuit transformers can vitallyaffect the performance and life of many electricalcomponents in a refrigeration or air conditioningsystem.An inadequate transformer supplying abnormally lowvoltage to the control circuit will result in improperoperation of contactors and/or motor starters due tochattering or sticking contacts, burned holding coils,or failure of contacts to properly close. Since any ofthese conditions can cause eventual system failure andpossible damage to the compressor, control transformersmust be properly sized.Even though a proper size transformer has beenselected, care must be taken to avoid excessive voltagedrop in a low voltage control circuit. When using a 24volt system with a remote thermostat, wire of sufficientcurrent carrying capacity must be installed between thetransformer and the thermostat .According to NEMA standards, a solenoid or contactormust operate satisfactorily at a minimum of 85% of ratedvoltage. Allowing for a line voltage fluctuation of plus orminus 10% which can occur on electric utility systems,the voltage drop of the transformer and connecting wiringmust be limited to 5% to insure a minimum of 85% ofrated voltage at the magnetic device.A transformer works on the magnetic induction principle,has no moving parts, and normally will have a long andtrouble free life. However, overloading of a transformerresults in excessive temperatures which will cause rapiddeterioration of the insulation and eventual failure of thetransformer coils.A control circuit transformer will not overheat, nor will itssecondary output voltage drop below 95% of its ratedvoltage if:© 1967 Emerson Climate Technologies, Inc.All rights reserved.8-3

1. The continuous VA (volt-amperes) capacity of thetransformer is equal to or greater than any continuousVA load that can occur in the system.2. The inrush VA capacity of the transformer is equal toor greater than the maximum VA load that can occurfor any combination of sealed and/or inrush load.(A sealed load is the terminology used to describea component load drawn through closed or sealedcontacts, after the inrush current has returned tonormal operating conditions.)Selection Procedure1. To select the proper transformer, the followinginformation is necessary:a. A list of all components in the control circuit.b. The sealed VA and watts for each.c. The inrush VA and inrush watts for each.Note: The VA and watts of magnetic devices will varywith each manufacturer, so it is necessary to obtainexact information on the components to be used.Since not all of the inrush data is included in catalogs,it will be necessary to contact representatives ofcomponent manufacturers for information whendesigning control circuits.2. The continuous VA requirement is determined bycombining the sealed VA of all components in thecircuit which can be energized at one time.3. The inrush VA capacity of a transformer is determinedby two factors — the VA inrush and the inrushload power factor. Each transformer manufacturerpublishes rating charts showing the inrush capacityof each size transformer in terms of the per cent ofrated load at varying secondary output voltages andvarying power factors. Since output voltages lowerthan 95% are not acceptable, the only variable tobe determined is the power factor.The maximum VA inrush is found by combining theinrush VA that can occur with the maximum sealedVA that can occur simultaneously. To determine theinrush load power factor, divide the maximum inrushwatts by the maximum inrush VA.Examples Of Transformer SelectionFigure 44 is typical of one manufacturer’s curves showingthe inrush capacity of three different transformers at95% of rated output voltage for varying power factors.To illustrate the selection procedure, assume a controltransformer is to be selected from Figure 44 for thefollowing control circuit:Example No.1Sealed Sealed Inrush InrushVA Watts VA Watts1 - 60 amp contactor 25 7 165 1241 - oil pressuresafety switch 25 25 25 251 -10 amp fan starter 8 5 58 12Assume the compressor is cycling on the contactor,and the oil pressure safety switch heater element isenergized whenever the compressor oil pressure isbelow 15 psig. The fan starter is used to energize a fancircuit at the same time the compressor is energized.Therefore, the contactor and the fan starter would be acontinuous load, and the inrush load would be the inrushVA of the contactor and the fan starter, plus the heaterload of the oil pressure safety switch.A. Continuous VA requirementContactor 25 VAFan Starter 8 VATotal 33 VAAny transformer with a rating of 33 VA or more wouldhandle the continuous load, so the 60 VA transformeris satisfactory.B. Inrush VA RequirementVA WattsContactor 165 124Fan Starter 58 12Oil PressureSafety Switch 25 25Total 248VA 161 Watts161 WattsPower factor equals 248 VA or .65Although the continuous VA requirement could be metwith the 60 VA transformer shown on Figure 44 it wouldrequire the 140 VA transformer to satisfy the inrush VArequirement, and the larger size must be used.Example No.2Assume the same conditions as in Example No.1 exceptthat the compressor has two 60 amp contactors foracross the line operation.(continued on p. 8-6)8-4© 1967 Emerson Climate Technologies, Inc.All rights reserved.

© 1967 Emerson Climate Technologies, Inc.All rights reserved.8-5

A. Continuous VA requirement2 Contactors 50 VAFan Starter 8 VATotal 58 VAThe 60 VA transformer in Figure 44 is adequate for thecontinuous load.B. Inrush VA requirementVA Watts2 Contactors 330 VA 248 WattsFan Starter 58 VA 12 WattsOil PressureSafety Switch 25 VA 25 WattsTotal 413 VA 285 Watts285 WattsPower factor equals 413 VA or .69Referring to Figure 44 the 140 VA transformer does nothave enough capacity for the inrush VA requirement,and the 200 VA transformer must be used.These examples clearly indicate that the continuousVA requirement of the control circuit may be greatlyexceeded by the inrush VA requirement, and both factorsmust be considered in selecting transformers.Transformer manufacturers use a standard 20% powerfactor in their catalog literature for determining themaximum inrush VA rating of a transformer. Since theinrush power factor of contactor coils may be muchhigher than 20%, and since the resistive load of the oilpressure safety switch will increase the overall powerfactor, a typical compressor control circuit may have aninrush power factor greatly in excess of 20%.The allowable inrush VA load on a transformer decreaseswith an increase in the power factor (see Figure 44) andthe use of an incorrect power factor may result in anundersized transformer. To properly size a transformer,the power factor must be calculated for the componentsto be used.8-6© 1967 Emerson Climate Technologies, Inc.All rights reserved.

Section 9MOTORSElectric motors are used as the power source on the greatmajority of refrigeration compressors, and practically allare now alternating current (A. C.) motors. The followingdiscussion is limited to those motors of interest for drivingrefrigeration compressors.Nearly all motors used for refrigeration applications areinduction motors, the name coming from the fact that thecurrent in the moving part of the motor is induced, themoving component having no connection to the sourceof current. The stationary part of an induction motor iscalled the stator, and the moving part the rotor. The statorwindings are connected to the power source, while therotor is mounted on the motor shaft, the rotation of therotor providing the motor driving power source.MOTOR TEMPERATUREThe first law of thermodynamics stated that energy cannotbe either created or destroyed, but may be convertedfrom one form into another. The motor receives electricalenergy from the power source, but because of frictionand efficiency losses, only a part of this input energy canbe turned into mechanical output energy. The balanceof the input energy is converted to heat energy, andunless this heat is dissipated, the temperature within themotor windings will rise until the insulation is destroyed.If a motor is kept free from contamination and physicaldamage, heat is practically the only enemy that candamage the windings.The amount of heat produced in the motor dependsboth on the load and on motor efficiency. As the loadis increased, the electrical energy input to the motorincreases. The percentage of the power input convertedto heat in the motor depends on motor efficiency,decreasing with an increase in efficiency, and increasingas efficiency decreases.The temperature level, which a motor can tolerate,depends largely on the type of motor insulation and thebasic motor design, but the actual motor life is determinedby the operating conditions to which it is subjected duringuse. If operated in a proper environment, at loads withinits design capabilities, a well designed motor shouldhave an indefinite life. Continuous overloading of a motorresulting in consistently high operating temperatures willmaterially shorten its life.OPEN TYPE MOTORS AND BELT DRIVESOpen type motors may be used for compressor drive witheither a belt drive or a direct drive arrangement, but withthe continued development of hermetic and accessiblehermeticmotor-compressor design, the use of opentype motors has declined rapidly. Open type motors forcompressor drives should be selected conservativelysince open type motors do not have the generousoverloading safety factor found in most motors used inhermetic and accessible hermetic compressors.V-belts are made in several different industryclassifications, which have been standardized forinterchangeability. For refrigeration use, fractionalhorsepower industrial belts and conventional industrialbelts are the two types commonly used. The fractionalhorsepower belts are more flexible and are well adaptedto small radius drives in the smaller horsepowerrange.The conventional industrial belts have a higherhorsepower rating for heavier loads. Fractionalhorsepower “4L” and conventional “A” belts have acomparable cross section and may be used on thesame size pulley, while fractional horsepower “5L” andconventional “B” belts are similarly interchangeable.For belt driven compressors, the compressor speed isdetermined by the size of the motor pulley, since thecompressor pulley (flywheel) is normally fixed. Therelative speeds of the motor and compressor are indirect relation to the diameter of the motor pulley andthe compressor flywheel, but for accurate calculation,the pitch diameter of the pulley must be used ratherthan the outside pulley diameter (O. D.). The pitchdiameter makes allowance for the fact that the V-beltrides partially inside the pulley O. D. For drives using “A”and “4L” section belts, the pitch diameter may be takenas pulley O. D. less 1/4”, and for “B” and “5L” sectionbelt drives, pulley O. D. less 3/8”.© 1967 Emerson Climate Technologies, Inc.All rights reserved.9-1

The desired pulley size or the resulting compressor speed may then be calculated from the following relation:Compressor Speed, RPM =Pitch Diameter, Motor Pulley, In. =(Motor Speed, RPM) x (Pitch Diameter, Motor Pulley, In.)(Pitch Diameter, Compressor Pulley, In.)(Compressor Speed, RPM) x (Pitch Dia., Compressor Pulley, In.)(Motor Speed, RPM)For example, to find the motor pulley diameter required when a 1750 RPM motor is to be used to drive a compressorhaving an 8” pitch diameter compressor pulley, when the desired compressor speed is 500 RPM, proceed asfollows:P.D., Motor Pulley =500 RPM Com. Speed x 8” P. D., Comp. Pulley1750 RPM, Motor Speed= 500 x 81750 = Approximately 2 1/4 inches P. D.For an “A” belt driveMotor Pulley O. D. = 2 1/4 inches P.D. + 1/4 inch = 2 1/2 inches O.D.For a “B” belt driveMotor Pulley O. D. = 2 1/4 inches P.D. + 3/8 inch = 2 5/8 inches O.D.HERMETIC MOTORSIn hermetic and accessible-hermetic motor-compressors,the motor is mounted directly on the compressorcrankshaft, and is hermetically sealed within thecompressor body. Aside from the economies inherent inthis type of construction, the greatest advantage is thatthe motor can be cooled by a variety of means, such asair, water, or refrigerant vapor. Sealing the motor in thecompressor body eliminates the troublesome problemof sealing the crankshaft so that the power may betransmitted without refrigerant leaks. By designing amotor for the specific application, and controlling motortemperature closely, a motor may be matched to a givenload with the result that the motor output can be utilizedat its maximum capability, while maintaining a generoussafety factor considerably above that available withstandard open type motors.NAMEPLATE AMPERAGEOn open-type motors standard NEMA horsepowerratings are used to identify a motor’s power outputcapability. Because of industry practice, this nominalhorsepower classification has carried over into hermeticmotor identification, but it may be misleading whenapplied to this type of motor. With controlled cooling andmotor protection sized for the exact load, a hermeticmotor may be operated much closer to its maximumability, so a given motor may be capable of much greaterpower output as a hermetic motor than an equivalentopen motor. The amperage draw and watts of powerrequired are much better indicators of hermetic motoroperation.Each Copeland® brand motor-compressor carries onits nameplate ratings for both locked rotor and full loadamperes. The designation full load amperage persistsbecause of long industry precedent, but in reality amuch better term is nameplate amperage. On all weldedcompressors, on all new motors now being developedfor Copelametic® compressors, and on most of themotors developed with inherent protection or internalthermostats, nameplate amperage has been arbitrarilyestablished as 80% of the current drawn when themotor protector trips. The 80% figure is derived fromstandard industry practice of many years’ standing insizing motor protective devices at 125 % of the currentdrawn at rated load conditions.In order for the motor to meet Emerson ClimateTechnologies, Inc. standards, the maximum allowablecurrent must be beyond the prescribed operating limitsof the compressor, and is determined during qualificationtests by operating the compressor at establishedmaximum load conditions and lowering the supplyvoltage until the protector trip point is reached. Useof the standard 80% factor enables the service andinstallation engineer to safely size wiring, contactors,or other external line protective devices at 125% of thenameplate rating, since the motor-compressor protectorwill not allow the amperage to exceed this figure.In most instances, the motor-compressor is capableof performing at nominal rating conditions at less thanrated nameplate amperage. A given motor frequentlyis used in various compressor models for air-cooled,9-2© 1967 Emerson Climate Technologies, Inc.All rights reserved.

suction-cooled, water-cooled, high temperature, mediumtemperature, low temperature, R-12, R-22, or R-502applications as required. Obviously on many applicationsthere will be a greater safety factor than on others.This does not mean that every compressor may beoperated continuously at a load greatly in excess of itsnameplate rating without fear of failure. Motor amperageis only one factor in determining a compressor’s operatinglimitations. Discharge pressure and temperatures,motor cooling, and torque requirements are equallycritical. Safe operating limits have been establishedfor each compressor, and are published on compressorspecification sheets.VOLTAGE AND FREQUENCYAlthough electric energy distributed in the United Statesis 60 cycle, distribution voltages are not standardized.Single phase voltages may be 115, 208, 220, 230, or240, and most utilities reserve the right to vary thesupply voltage plus or minus 10% from the nominalrating. Three phase voltage may be 208, 220, 240, 440,460, or 480, again plus or minus 10%. Unless motorsare specifically designed for the voltage range in whichthey are operated, overheating may result.Most motors may be operated at the voltage on themotor nameplate, plus or minus 10% without dangerof overheating, but in order to allow more flexibility ofoperation, extended voltage range motors are now beingdeveloped where the usage warrants this action. Forexample, a three phase motor nameplated 208/240 voltsis satisfactory for operation from 187 volts to 264 volts,and a three phase motor nameplated 440/480 volts maybe operated from 396 volts to 528 volts.In many parts of the world, the electrical power supplyis 50 cycle rather that 60 cycle. If both voltage andfrequency supplied to a motor vary at the same rate,operation of a given motor at the lower frequencycondition within narrow limits is satisfactory in somecases. For example, a 440 volt, 3 phase, 60 cycle motorwill operate satisfactorily on 380 volt, 3 phase, 50 cyclepower supply.However, in some 50 cycle applications, the relationshipbetween voltage and frequency is such that standard60 cycle motors cannot be used unless the motorcharacteristics are suitable for 50 cycle operation, andthis can be determined only by test. On most singlephase 50 cycle applications, specially wound 50 cyclemotors are required.THREE PHASE MOTORSThree phase motors are wound with 3 separate windingsor phases. Each of the windings is 120° out of phase withthe other windings, which results in a very high startingtorque motor requiring no supplemental mechanismsor devices for starting. The direction of rotation ofthe motor may be changed by reversing any two lineconnections.Because three phase motors can utilize smaller wire sizesand therefore are smaller, they are used on almost allapplications larger than 5 HP, and if three phase poweris available, are frequently preferred for any load largerthan fractional horsepower applications.SINGLE PHASE MOTORSA single phase motor has but one running winding orphase, and basically is not a self starting motor. Oncestarted, it will run as a pure induction motor. In orderto provide starting torque, a second winding called thestarting winding is provided, which normally has greaterresistance than the running winding. The differentvariations of single phase motors are primarily due tothe different starting arrangements used.If the start winding remains in the circuit during operationit would be damaged by excessive heat. Therefore, thestarting winding is removed from the circuit as the motorapproaches rated speed by either a potential relay, acurrent relay, or a centrifugal switch.A current relay is normally open when de-energized,and the coil is wound so that the contacts will closewhen starting current is being drawn by the motor, butwill drop out when the current approaches normal fullload conditions. Therefore, the current relay is closedonly during the starting cycle.A potential relay is normally closed when de-energized,and the coil is designed to open the contacts only whensufficient voltage is generated by the start winding. Sincethe voltage or back-EMF generated by the start winding isproportional to the motor speed, the relay will open onlywhen the motor has started and is approaching normalrunning speed. The illustrations show the schematicwiring with the motor in operation so the potential relayis in the energized position.SPLIT PHASE MOTORSOn a split phase motor, the running winding and startwinding are in parallel, and are spaced 90° apart. The© 1967 Emerson Climate Technologies, Inc.All rights reserved.9-3

un winding is wound with relatively heavy wire, whilethe start winding is wound with fine wire and has a muchgreater resistance than the run winding. The combinationof greater resistance and physical displacement resultsin the start winding being slightly out of phase with therun winding, and thus produces sufficient magnetic forceto cause the rotor to rotate.Figure 45 illustrates a split phase motor schematicelectrical diagram with a current relay to break thestart winding circuit when the compressor has reachedoperating speed.The starting torque of a split phase motor is low, thestarting current is high, and the efficiency is relativelylow. As a result, this type of motor is generally limited tocapillary tube systems in small fractional HP sizes.CAPACITOR START - INDUCTION RUN MOTORS(CSIR)This motor is similar to the split phase motor inconstruction except for the method used to obtain thephase displacement necessary for starting. In the splitphase motor, the phase displacement is due to a higherresistance in the start winding. In the capacitor startmotor, the necessary phase displacement is achievedthrough the use of a capacitor connected in series withthe starting winding. A capacitor start-induction runschematic electric diagram is shown in Figure 46.The starting winding is removed from the circuit after themotor is started by the potential relay or current relayas before. This type motor has a high starting torque,and therefore is suitable for applications where unequalpressures may be encountered on start up. Because ofthe low power factor of this type motor, its use is usuallylimited to fractional horsepower applications.CAPACITOR START - CAPACITOR RUN MOTORS(CSR)By connecting a running capacitor in parallel with thestarting capacitor (R to S terminals) as shown inFigure 47 the motor is strengthened because the startwinding is loaded in phase with the main winding afterthe start capacitor is disconnected, which permits thestarting winding to carry part of the running load. Therunning capacitor strengthens the motor, improvesthe power factor, reduces motor current, increasesthe efficiency, and decreases the temperature of themotor under design conditions. However, the motormust be designed for operation with a run capacitor,and a capacitor start-induction run motor usually is notsuitable for conversion to capacitor start-capacitor runoperation.Normally current relays are not recommended for usewith capacitor start-capacitor run motors because ofthe danger of the running capacitor discharging to the9-4© 1967 Emerson Climate Technologies, Inc.All rights reserved.

start capacitor through the current relay when it closes.The high voltage built up on the running capacitorcan cause the current relay contacts to arc, possiblywelding the contacts and causing compressor failure.If a current relay is used with a capacitor start-capacitorrun motor, a resistor should be installed between therunning capacitor and start capacitor to prevent a highcurrent flow to the start capacitor on start-up. Thiscondition does not occur on systems equipped withpotential relays since the contacts are normally closedat start-up, and the voltage build-up on both start andrun capacitors is similar.The run capacitor is in the circuit continuously and isdesigned for continuous operation whereas the startcapacitor is used only momentarily each time the motorstarts and is designed for intermittent duty.Capacitor start-capacitor run motors have high efficiency,high power factor, and high starting torque and are usedin single phase motors from fractional HP through 5HP in size.PERMANENT SPLIT CAPACITOR MOTORS (PSC)For some applications not requiring high starting torque,a motor with only a running capacitor is desirable.Because of the elimination of the start capacitor andrelay, this type of motor is economical and efficient, buthas low starting torque. Its use is limited to systems onwhich pressures are equalized prior to start up, and isprimarily used in air conditioning and small commercialapplications.A permanent split capacitor motor schematic electricaldiagram is illustrated in figure 48. It is identical to thecapacitor start-capacitor run diagram without the startingcapacitor and relay. If increased starting torque isrequired, a starting capacitor and relay assembly canbe added to this motor, making it identical to a capacitorstart-capacitor run motor in operation.DUAL VOLTAGE MOTORSCertain Copeland® brand three phase motors are woundwith two identical stator windings which are connectedin parallel on 208 or 220 volt operation, and in seriesfor 440/480 volt operation. Internal connections of thistype of motor are shown in Figure 49.These models have two parallel windings with nine leadswhich must be connected correctly for the voltage ofthe power supply. If the windings are connected out ofphase, or if the jumper bars are not positioned correctly,motor overheating and possible failure can occur.© 1967 Emerson Climate Technologies, Inc.All rights reserved.9-5

TWO PHASE MOTORSTwo phase power is still used in a few isolated areas,and specially wound two-phase motors are required foruse on this type of power supply. These motors havetwo parallel windings, and are similar to three phasemotors in their operation. Capacitors and starting relaysare not required. The motor is started directly acrossthe line by means of a special 4 pole contactor . Thephase windings are connected in parallel from the twophase three or four wire power supply.9-6© 1967 Emerson Climate Technologies, Inc.All rights reserved.

Section 10STARTING EQUIPMENT AND MOTOR PROTECTORSSince hermetic motors must operate under a wide rangeof operating conditions, and vary in size from fractionalhorsepower to 35 HP and larger, a wide variety of startingequipment is used.CONTACTORS AND STARTERSA contactor is a load current carrying device, which makesand breaks to start and stop the compressor motor. Astarter is merely a contactor with motor protective devicesmounted in a common enclosure.On single phase motors up to 3 HP in size, the motorcurrent is often low enough to be handled by the contactsin the low pressure control or thermostat, and no separatecontactor is required. As the motor size increases, theamperage draw increases beyond the range of smallcontrol apparatus, and the motor current must be handledthrough the contacts of a starter or contactor, while thecontrol makes and breaks a pilot circuit which energizesthe coil of the contactor .For motor-compressors whose power requirementsare such that contactors are required, it is essentialthat the contactors used are adequately sized for theattached load. The rating of the contactor for both fullload amperes and locked rotor amperes must be greaterthan the nameplate rating of the motor-compressor plusthe nameplate rating of any fans or other accessoriesalso operated through the contactor .NEMA general purpose type contactors are built for themost severe industrial usage, and are designed for aminimum life of 2,000,000 cycles. Because they mustbe adaptable to any usage, general purpose contactorshave a large safety factor, and as a result are bothlarge and costly. For refrigeration and air conditioningapplications, a life of 250,000 cycles is entirely adequate,so the physical construction can be lighter, and the costof the contactor correspondingly less.To meet the specific needs of the refrigeration and airconditioning industry, electrical equipment manufacturershave developed definite purpose contactors. Thesecontactors are rated in amperes, and when selectedproperly for the load, are smaller and more economicalthan the general purpose contactor. Since compressorcontactors are frequently subjected to quick recycling,the contacts must be large enough for satisfactory heatdissipation in order to prevent contactor overheating.Overheating of the contacts may cause sticking andsingle phasing, and can cause a motor failure eventhough the motor overload protectors trip and open thecontrol circuit.In order to insure that definite purpose contactorsare properly applied to Copeland® brand motorcompressorswith pilot circuit protection, the contactormust meet Emerson Climate Technologies, Inc. minimumperformance requirements.CAPACITORSAn electrical capacitor is a device which stores electricalenergy. They are used in electric motors primarily todisplace the phase of the current passing through thestart winding. While a detailed study of electrical theoryis beyond the scope of this manual, capacitors in amotor circuit provide starting torque, improve runningcharacteristics and efficiency, and improve the powerfactor.The amount of electrical energy a capacitor will holddepends on the voltage applied. If the voltage isincreased, the amount of electrical energy stored in thecapacitor is increased. The capacity of a capacitor isexpressed in microfarads (MFD) and is dependent onthe size and construction of the capacitor.The voltage rating of a capacitor indicates the nominalvoltage at which it is designed to operate. Use of acapacitor at voltages below its rating will do no harm. Runcapacitors must not be subjected to voltages exceeding110% of the nominal rating, and start capacitors must notbe subjected to voltages exceeding 130% of the nominalrating. The voltage to which a capacitor is subjected is notline voltage, but is a much higher potential (often calledelectromotive force or back EMF) which is generatedin the start winding. On a typical 230 volt motor, thegenerated voltage may be as high as 450 volts, andis determined by the start winding characteristics, thecompressor speed, and the applied voltage.Capacitors, either start or run, can be connected eitherin series or parallel to provide the desired characteristicsif the voltage and MFD are properly selected. When twocapacitors having the same MFD rating are connectedin series, the resulting total capacitance will be one halfthe rated capacitance of a single capacitor. The formulafor determining capacitance (MFD) when capacitors areconnected in series is as follows:© 1967 Emerson Climate Technologies, Inc.All rights reserved.10-1

1 = 1 + 1MFD total MFD1 MFD2For example, if a 20 MFD and a 30 MFD capacitor areconnected in series, the resultant capacitance will beMFDt = 12 MFD1 1 1MFDt = MFDl + MFD21 1 1MFDt = 20 + 301 5 1MFDt = 60 = 12The voltage rating of similar capacitors connectedin series is equal to the sum of the voltage of thetwo capacitors. However, since the voltage acrossindividual capacitors in series will vary with the ratingof the capacitor, for emergency field replacements it isrecommended that only capacitors of like voltage andcapacitance be connected in series to avoid the possibilityof damage due to voltage beyond the capacitor limits.When capacitors are connected in parallel, their MFDrating is equal to the sum of the individual ratings. Thevoltage rating is equal to the smallest rating of theindividual capacitors.It is possible to use any combination of single, series,or parallel starting capacitors, with single or parallelrunning capacitors (running capacitors are seldomused in series).START CAPACITORSStart capacitors are designed for intermittent service only,and have a high MFD rating. Their construction is of theelectrolytic type in order to obtain the high capacity.All standard Copeland® brand starting-capacitors aresupplied with bleed-resistors securely attached andsoldered to their terminals as shown in Fig. 51.The use of capacitors without these resistors probablywill result in sticking relay contacts and/or erratic relayoperation – especially where short cycling is likely tooccur.This is due to the starting capacitor discharging throughthe relay contacts as they close, following a very shortrunning cycle. The resistor will permit the capacitorcharge to bleed down at a much faster rate, preventingarcing and overheating of the relay contacts.The use of capacitors supplied by Emerson ClimateTechnologies, Inc. is recommended, but in case of anemergency exchange, a 15,000 -18,000 ohm, two wattresistor should be soldered across the terminals of eachstarting capacitor. Care should be taken to prevent theirshorting to the case or other nearby metallic objects.If sticking contacts are encountered on any starting relaythe first item to check is the starting capacitor resistors.If damaged, or not provided, install new resistors, andclean the relay contacts or replace the relay.Suitable resistors can be obtained from any radio partswholesaler.RUN CAPACITORSRun capacitors are continuously in the operating circuit,and are normally of the oil filled type. The run capacitorcapacitance rating is much lower than a start capacitor.Because of the voltage generated in the motor startwinding, the run capacitor has a voltage across itsterminals greater than line voltage.The starting winding of a motor can be damaged by ashorted and grounded running capacitor. This damageusually can be avoided by proper connection of therunning capacitor terminals.The terminal connected to the outer foil (nearest thecan) is the one most likely to short to the can and begrounded in the event of a capacitor breakdown. It is10-2© 1967 Emerson Climate Technologies, Inc.All rights reserved.

for full voltage starting. However, due to power companylimitations on starting current, some means of reducingthe inrush starting current on larger horsepower motorsis occasionally necessary. This is particularly true inother countries, and is necessary in some sections ofthe United States and Canada. The principal reasonfor these restrictions is to prevent light flicker, televisioninterference, and undesirable side-effects on otherequipment because of the momentary voltage dip.The reduced voltage start allows the power companyvoltage regulator to pick up the line voltage after partof the load is imposed, and thus avoids the sharpervoltage dip that would occur if the whole load werethrown across the line.identified and marked by most manufacturers of runningcapacitors. See Fig. 52.From the supply line on a typical 115 or 230 volt circuit,a 115 volt potential exists from the “R” terminal toground through a possible short in the capacitor. (Seewiring diagram Fig. 53.) However, from the “S” or startterminal, a much higher potential, possibly as high as400 volts, exists because of the EMF generated in thestart winding. Therefore, the possibility of capacitorfailure is much greater when the identified terminal isconnected to the “S” or start terminal.THE IDENTIFIED TERMINAL SHOULD ALWAYSBE CONNECTED TO THE SUPPLY LINE, OR “R”TERMINAL, NEVER TO THE “S” TERMINAL. Thisapplies to PSC as well as capacitor-start, capacitor-runmotors.If connected in this manner, a shorted and groundedrunning-capacitor will result in a direct short to groundfrom the “R” terminal and will blow line fuse No.1. Themotor protector will protect the main winding fromexcessive temperature.If, however, the shorted and grounded terminal isconnected to the start winding terminal “S”, current willflow from the supply line through the main winding andthrough the start winding to ground. Even though theprotector may trip, current will continue to flow throughthe start winding to ground, resulting in a continuingtemperature rise and failure of the starting winding.REDUCED VOLTAGE STARTINGFull voltage “across-the-line” starting is the leastexpensive way to start a three-phase motor, and allmotors in Copeland® brand compressors are designedSome electrical utilities may limit the inrush current drawnfrom their lines to a given amount for a specified periodof time. Others may limit the current drawn on start-upto a given percent of locked rotor current.Unloading the compressor can be helpful in reducingthe starting and pull-up torque requirement, and willenable the motor to accelerate quickly. But regardless ofwhether the compressor is loaded or unloaded, the motorwill still draw full starting amperage for a small fractionof a second. Since the principal objection usually is tothe momentary inrush current drawn under locked rotorconditions when starting, unloading the compressor willnot always solve the problem. In such cases some typeof starting arrangement is necessary that will reduce thestarting current requirement of the motor.Starters to accomplish this are commonly known asreduced voltage starters, although in two of the mostcommon methods the line voltage to the motor is notactually reduced. Since manual starting is not feasiblefor refrigeration compressors, the only type of startersto be considered are magnetic.There are five types of magnetic reduced voltage starters,each of which has certain characteristics, which aredesirable for specific applications.1. Part winding2. Star-Delta3. Autotransformer4. Primary Resistor5. Reduced voltage step starting accessoryAs the starting current is decreased, the starting torquealso drops, and the selection of the starter to be usedmay be limited by the compressor torque requirement.The maximum torque available with reduced voltagestarting is 64% of full-voltage torque, which can beobtained with an autotransformer starter, while partwinding starters deliver approximately 45% of full-© 1967 Emerson Climate Technologies, Inc.All rights reserved.10-3

voltage torque, and star-delta starters only 33%. ForCopeland® brand motor-compressors without unloaders,a starting torque of 45% of full-voltage torque or higheris recommended. The use of an unloaded start is helpfulin critical applications, and for low torque starting suchas encountered in star-delta starters, an unloaded startis essential if the compressor is to start under reducedvoltage conditions.However, it is not necessary for the motor-compressorto start and accelerate under the reduced voltage phaseof starting to accomplish the objective of reducing thepeak starting current. By energizing the motor a stepat a time, the power company requirements may besatisfied, while at the same time by keeping the timedelay between steps in starting to a minimum, damage tothe compressor can be avoided. It is of course desirablefor the compressor motor to start and accelerate under10-4© 1967 Emerson Climate Technologies, Inc.All rights reserved.

educed voltage starting conditions to realize the majorbenefits of this type of starting arrangement.1. Part Winding StartThis is not a true reduced voltage start, but it accomplishesthe same job - limiting inrush current - by utilizing onlypart of the motor windings. Since it uses both the startand run contactors to carry the motor current duringoperation, it costs less than the other types.To utilize part winding start, the motor must have a dualwinding. Copeland® brand 208/220/440 volt, 3 phasemotors are wound with two identical stator windingswhich are connected in parallel on 208 or 220 voltoperation. For part winding start, the first step utilizesonly one winding or 1/2 of the stator, and these motorsmay be used whenever part winding start is requiredon 208 or 220 volt power. Part winding start cannot beused on these motors when used on 440 volts, sincethe entire winding must be connected in series for 440volt power .Copelametic® model 4R and 6R compressors arecurrently available with dual wound motors, and some4R and 6R models are available with specially woundmotors for part winding start on 550 volts.Basically all that is required for part winding start aretwo contactors, each capable of carrying the winding’sfull load and locked rotor current requirement, with atime delay between the contactors. When the starteris energized, the first magnetic contactor closes andputs half of the motor winding across the line. A presettime delay relay is energized at the same time, and atthe completion of the timing cycle, the second magneticcontactor closes and puts the second half of the motorwinding in parallel with the first.The normal Copeland® brand compressor motorprotectors must be used. Where current sensingprotectors are required, they must be installed in atleast two phases of each contactor. Motors equippedwith a Thermotector need no other external protection.To prevent tripping of the protectors during starting, thetime delay between the first and second contactor mustbe well within the protector’s tolerance for locked rotorconditions, and a time delay device having a time cyclesetting of one second ± 10% is required.The exact current and torque characteristics of a motorwill vary with design. For Copeland® brand motorcompressorsstarting on one winding, the motor willdraw approximately 65% of the normal across-the-linestarting current, and produce approximately 45% of thenormal starting torque. Under heavily loaded conditions,it is possible that the motor may not start until thesecond winding is energized, or if it does start, it maynot accelerate. An unloaded start may be desirableunder extreme conditions.On part winding start applications, occasionally anelectrical starting noise or “growl” of short durationmay be noticed. This occurs when the first half windingstarts the motor, but is unable to accelerate it beyonda few hundred rpm. As soon as the second winding isenergized, the motor instantly accelerates, and the noisedisappears. Since the time delay between windings isno greater than one second, the noise duration is veryshort.The noise will vary with voltage, speed, pressuredifferential, motor horsepower, and will vary slightlyfrom compressor to compressor. In addition, motorssupplied by different sources may have slight differencesin motor characteristics, and the resulting sound maybe slightly different.Occasionally service personnel mistake the starting noisefor bearing drag. The starting noise is quite normal, willbe more pronounced on larger motors, and does notharm the compressor In any way.2. Star-Delta StartingFor star-delta starting (also referred to as wye-delta)a specially wound motor is required with both ends ofeach phase winding brought out to terminals. By meansof contactors a motor designed for normal operation indelta is first connected in star, and after a predeterminedtime delay, the star connection is changed to delta. Thisstarting arrangement is relatively simple and inexpensive,and is widely used in Europe.Recently three phase, 50 cycle motors have beendeveloped for most Copeland® brand compressors 7½HP and larger specially wound for star-delta starting.Leads were brought out from both ends of each phaseso that the motors could be connected in either star ordelta. Motors are available for star-delta start connectionson either 380 volt, 50 cycle, 3 phase or 220 volt, 50cycle, 3 phase circuits.When a motor designed for delta operation is connectedin star, the voltage across each phase is reduced to 58%of normal, and the motor develops 1/3 of the normalstarting torque. The inrush current in star is 1/3 of normalinrush current in delta.Star-delta starting is suitable for low torque starting dutyonly. To insure starting on the star connection, somemeans of pressure equalization across the compressor(continued on p. 10-7)© 1967 Emerson Climate Technologies, Inc.All rights reserved.10-5

10-6© 1967 Emerson Climate Technologies, Inc.All rights reserved.

prior to starting is essential. Unloading the compressorduring the starting phase is also recommended.In order to eliminate the objectionable flicker or jump incurrent occurring during the change from star to delta,closed transition starters employ an additional contactorand three resistors which are utilized to keep the motorconnected to power through the resistors during thetransition period. Since the transition period is less than1/10 of a second in duration, the resistors can be relativelysmall. Closed transition starting is recommended toprevent objectionable surges of current.Since the relation between line current and phase currentwill vary with the switch from star to delta connections,motor overload protectors must be mounted in themotor winding circuit. Compressors equipped withThermotectors (fast response thermostats) require noadditional external line protection since the Thermotectorprotects by sensing an increase in motor windingtemperature. For compressors requiring externalcurrent sensing protectors, specially sized protectorsare required, and the Emerson Climate Technologies,Inc. Application Engineering Department should becontacted for specifications.3. Autotransformer StartersAutotransformer type starters reduce the voltage acrossthe motor terminals during the starting and acceleratingperiod by first connecting the motor to taps on thetransformer, and then after a time delay, switching themotor connection across the line.Due to the lower starting voltage, the motor will drawless current and will develop less torque than if the motorwere connected across the line.Because of the transformer action, the current in themotor windings is actually greater than the line currentby a proportion equal to the ratio of transformation, afterallowing for the autotransformer excitation current. Thisresults in a very flexible control system, since the startingcurrent inrush can be effectively limited as desired, whilethe starting torque per ampere of the line current is themaximum available from any reduced voltage starter.The autotransformer starter is the most complex and themost expensive of the reduced voltage starters, but ifhigh starting torque is required, it often is the only typethat will perform acceptably.Taps are provided on the transformer for various stagesof voltage reduction, with reductions of 80% and 65%of full line voltage normally available on most models.Closed circuit transition is recommended to preventhigh transient current when transferring from “start” to“run” conditions.© 1967 Emerson Climate Technologies, Inc.All rights reserved.10-7

Regular Copeland® brand motor protectors can bemounted in the leads to the compressor, or adequateprotection is provided by inherent protectors.Since no special winding is required in the motor,the autotransformer starter can be used with anyCopelametic® compressor. As with other types, the timedelay must be very brief to avoid tripping the protectorduring the starting process.4. Primary Resistor StartersIn many respects, the primary resistor starter is similarto the autotransformer type. The motor is connectedto line current through heavy resistors during the initialstarting step in order to reduce the voltage applied tothe motor windings. After a time delay, the resistorsare shorted out of the circuit, and the compressor isconnected across the line.However, since starting torque is proportional to thesquare of the voltage applied to the motor, the startingtorque falls off rapidly with the reduction of applied motorvoltage. The resistors act to prevent current surges, andprovide smooth acceleration of the motor once startingis accomplished, since the voltage drop across theresistors decreases as the motor comes up to speedand the inrush starting current decreases.No special motor windings are required, and regularCopeland® brand motor protectors can be used. As withthe autotransformer starter, this system can be appliedto any Copelametic® motor. The time delay must belimited to avoid tripping during starting.5. Reduced Voltage Step Starting AccessoryThe reduced voltage accessory panel was developedprimarily as a low cost, special purpose auxiliary to solvethe problem of light flicker caused by air conditionersof 3 HP and larger on single phase power lines. Thecost of special transformers and additional equipmentfor the power companies made some type of voltagelimitation device essential if service was to be continuedto the large single phase loads. Basically the reducedvoltage step starting accessory operates on the sameprinciple as the primary resistor starter, but it is moderatein cost, is used in conjunction with the regular contactor,and is designed for consumer applications rather thanindustrial use.The accessory inserts a resistance in series with themotor for approximately two seconds, after which a timingrelay energizes a contactor and shorts the resistors outof the circuit. The resulting torque is low, and the motorquite possibly will not start with the resistance in thecircuit, but the result is to break the inrush current intotwo steps which reduces light flicker to a level which isnot objectionable.MOTOR PROTECTIONSince hermetic motors may have to handle greatvariations in load for extended periods, close toleranceprotection must be provided to protect the motor in theevent of an overload. Standard heater coils in generalpurpose starters do not trip fast enough to protect themotor under locked rotor conditions. Although fast tripheater coils were developed to give faster response,their variation due to ambient temperature changesmakes them undependable under field conditions.Therefore specialized types of motor protection havebeen developed for refrigeration motor-compressors.In the event the compressor fails to start, and an internalprotector or thermostat trips, disconnecting the motor,it will normally reset very quickly after the initial trip. Ifseveral protector trips occur in succession, especiallywhen the motor is very hot from operation at heavilyloaded conditions, the motor temperature will rise to apoint exceeding the protector setting, and an off periodvarying from 20 minutes to one hour may be requiredfor the compressor motor to cool sufficiently so thatthe protector may reset. When this occurs, particularlyon across-the-line internally sealed protectors, servicepersonnel frequently assume that the motor has beendamaged and is inoperative, when in reality the motorprotection system is performing its intended duty. In theevent a compressor is checked and found to be very hotand inoperative, allow at least one hour for the motorto cool, and recheck after the cooling period beforechanging the compressor .Motor protection may be either of the line break orpilot circuit type. A line break protector incorporatescontacts which actually open the line directly when theprotector trips. A pilot circuit protector takes the motoroff the line indirectly by opening the holding coil circuitof the contactor, but the compressor protection is stilldependent on the contactor, since the compressor maybe subject to damage in case the contacts of a contactoror starter have stuck or welded, despite the fact that thepilot circuit protector may open.INTERNAL INHERENT LINE BREAK PROTECTORAn internal inherent line break protector is a devicecarrying full load current, responsive both to currentand/or temperature, which breaks line current if safelimits are exceeded.For three phase motors, the internal inherent protectoris connected in the center of a wye wound motor. It is10-8© 1967 Emerson Climate Technologies, Inc.All rights reserved.

located within the motor compartment on the motorwinding, and there are no external connections. Becauseof its location, the protector is sensitive to temperatureas well as current. When the protector opens, it breaksall three phases of the motor winding. Since this acrossthe-linedevice provides both over-current and lockedrotor protection, a contactor may be used instead of amotor starter. Internal inherent protectors are among thebest protection systems now available for hermetic andaccessible-hermetic motor-compressors, but becauseof the size of the device required, in larger motors, andalso because their usage is limited to single voltagemotors, their use is currently restricted to 7½ HP motorsand smaller.Single phase internal inherent protectors usually consistof contacts mounted on a bimetal disc which is sensitiveto both current passing through the protector and heatgenerated by the motor windings. They carry and breakfull line current in the same manner as three phaseprotectors, and have proved to be most satisfactory.EXTERNAL INHERENT PROTECTORThe external inherent protector is similar in constructionand operation to the internal inherent protector, but theexternal protector is mounted on the compressor bodyand senses motor current and compressor body heatrather than motor winding heat. Because the externalprotector is not subjected to refrigerant pressure, itscase is not hermetically sealed as is that of the internalinherent protector.INTERNAL THERMOSTATSOn some motor-compressors, particularly largerhorsepower sizes where inherent protectors cannotbe used, internal thermostats are located in the motorwinding. These are pilot circuit devices only, and reactonly to motor winding heat. When overheated they openthe control circuit, thereby stopping the compressor.These thermostats cannot be replaced in the field andare protected against excessive current in the controlcircuit by fuses.Because the temperature rise in motor windings duringlocked rotor conditions is both rapid and uneven, thethermostat often lags behind the winding temperature,and therefore some additional approved protectivedevice is necessary to protect the compressor motoragainst locked rotor conditions.EXTERNAL THERMOSTATSOn some older models of Copelametic® motorcompressors,an external thermostat is clamped to themotor housing to indirectly sense motor temperature.This is a pilot circuit device, and is similar to the internalthermostat in operation. Its sensitivity to temperature isreduced, and consequently the protection provided is notas good as that of the internal type. External thermostatsare no longer used by Emerson Climate Technologies,Inc. on current production.CURRENT SENSITIVE PROTECTORSExternal current sensing motor protectors are used inconjunction with internal thermostats to provide closetolerance locked rotor protection. They may be eitherthermal or magnetic in operation, carry full motor current,and are responsive to the current drawn by the motor.Normally these devices act to break the pilot circuit inthe event of a motor overload, but calibrated circuitbreaker types are available, which will break the linecurrent to the compressor.THERMOTECTORThe Thermotector is a quick reacting thermostatimbedded in the motor windings which senses motortemperature. Its current carrying capacity limits its use topilot circuit protection, but because of its fast response,it provides protection against overheating under lockedrotor as well as running conditions. Therefore it can beused with a contactor without external current sensingprotective devices, resulting in a simplified controlcircuit.SOLID STATE PROTECTORSVarious electronic solid state devices are now underdevelopment for use in motor protection, and it is probabletheir usage will increase. The control system design willvary, but normally the sensing device is a temperaturesensing element mounted on the motor windings inwhich the resistance changes with a change in motortemperature. The change in resistance when amplifiedby other solid state components acts to make or breakthe pilot circuit. As in the case with the Thermotectorthe quick response provides both running and lockedrotor current protection.FUSES AND CIRCUIT BREAKERSOn air conditioners having motor compressors with PSCmotors, it is possible that nuisance tripping of householdtype circuit breakers may occur. PSC motors have verylow starting torque, and if pressures are not equalizedat start up, the motor may require several seconds tostart and accelerate.This is most apt to occur where a short cycle of thecompressor can be caused by the thermostat making© 1967 Emerson Climate Technologies, Inc.All rights reserved.10-9

contact prematurely due to shock or vibration. Typicallythis can occur where the thermostat is wall mounted andcan be jarred by the slamming of a door.U. L. and most electrical inspection agencies now requirethat hermetic type refrigeration motor-compressorsmust comply with the National Electric Code maximumfuse sizing requirement. This establishes the maximumfuse size at 225% of the motor full load current, and bydefinition the motor-compressor nameplate amperageis considered full load current, unless this rating issuperseded by another on the unit nameplate.Since the motor protector may take up to 17 seconds totrip if the compressor fails to start, it is probable that astandard type fuse or circuit breaker sized on the basisof 225% of full load current may break the circuit prior tothe compressor protector trip, since locked rotor currentof the motor may be from 400% to 500% of nameplateamperage.To avoid nuisance tripping, Emerson ClimateTechnologies, Inc. recommends that air conditionerswith PSC motors be installed with branch circuit fuses orcircuit breakers sized as closely as possible to the 225%maximum limitation, the fuse or circuit breaker to be ofthe time delay type with a capability of withstanding motorlocked rotor current for a minimum of 17 seconds.EFFECT OF UNBALANCED VOLTAGE ANDCURRENT ON THREE PHASE MOTORPROTECTIONWhen external current sensing motor protectors areused to protect a three phase motor-compressor againstexcessive current draw and resulting motor overheating,unbalanced motor currents can seriously affect themotor protection system. While it is generally recognizedthat a break in one phase of a three phase distributionsystem can result in excessive amperage draw becauseof the resulting single phasing condition, another andequally serious hazard is the effect on amperage of anunbalanced voltage in the power supply.If single phasing occurs, the motor may stall unless lightlyloaded, and once stopped, it will not start, resulting inlocked rotor amperage draw. Under unbalanced voltageconditions, however, the motor will continue to operate,and motor protection may be dependent on the abilityof the protectors to sense the abnormally high runningcurrent or the increase in the motor temperature.A properly wound three phase motor connected to asupply source in which the voltages in each phaseare balanced at all times will have identical currents inall three phases. The differences in motor windings inmodern motors are normally so small that the effect onamperage draw is negligible. Under an ideal condition,if the phase voltages were always equal, a single motorprotector in just one line would adequately protect themotor against damage due to excessive amperagedraw. As a practical matter, balanced supply voltagesare not always maintained, so the three line currentswill not always be equal.Inherent line break motor protectors mounted at thecenter of the wye on wye wound motors provide protectionagainst all forms of voltage variation. However, on largermotors the size of the protector makes inherent protectorsimpractical, and many larger models of Copeland®brand compressors have a combination pilot circuitprotection system, consisting of internal thermostats andexternal current sensing protectors. Because internalthermostats are somewhat slow in reaction, and lagbehind the actual motor temperature in the event of afast temperature rise, locked rotor protection is providedby the external protector. Since in most cases adequateprotection can be provided by two leg current sensingprotection, and because of the size and cost of externalprotectors, the majority of compressors are installed withtwo leg protection, although the third protector can besupplied if desired. In order to determine if the motorwill be adequately protected under various abnormalconditions, an understanding of the inter-relation ofcurrent and unbalanced voltage is essential.When line voltages applied to a three phase inductionmotor are not the same, unbalanced currents will flow inthe stator windings. The effect of unbalanced voltagesis equivalent to the introduction of a “negative sequencevoltage” which is exerting a force opposite to that created10-10© 1967 Emerson Climate Technologies, Inc.All rights reserved.

with balanced voltages. These opposing forces willproduce currents in the windings greatly in excess ofthose present under balanced voltage conditions.Voltage unbalance is calculated as follows:% Voltage Unbalance = 100 xMax. Voltage Deviation from Average Volt.Average VoltageFor example, in Figure 57, assume voltage AB is 220volts, BC is 230 volts, and AC is 216 volts.Average Voltage =216 + 220 + 2303 = 222 VoltsMaximum Deviation = 230 - 222 = 8 Volts100 X 8% Voltage Unbalance = 222 = 3.6%As a result of the voltage unbalance, the locked rotorcurrent will be unbalanced to the same degree. However,the unbalance in load currents at normal operatingspeed may be from 4 to 10 times the voltage unbalance,depending on the load. With the 3.6% voltage unbalancein the previous example, load current in one phase mightbe as much as 30% greater than the average line currentbeing drawn by the other two phases.The NEMA Motors and Generators Standards Publicationstates that the percentage increase in temperature risein a phase winding resulting from voltage unbalance willbe approximately two times the square of the voltageunbalance.% Increase in Temperature =2 (Voltage Unbalance %)²Using the voltage unbalance from the previous example,the % increase in temperature can be estimated asfollows:% Increase in Temperature = 2(3.6 x 3.6) = 25.9%As a result of this condition, it is possible that one phasewinding in a motor may be overheated while the othertwo have temperatures within normal limits. If only twomotor protectors are being used, and the high currentwinding is not protected, ultimate motor failure mayoccur even though the protectors do not trip. Therefore,when installing external motor protectors for a motor inwhich only two of the three phases are to be protected,be sure the protectors are mounted in the phases withthe highest amperage draw.A common source of unbalanced voltage on a threephase circuit is the presence of a single phase loadbetween two of the three phases. (See Figure 58).A large unbalanced single phase load, for example alighting circuit, can easily cause sufficient variations inmotor currents to endanger the motor. If at all possible,this condition should be corrected by shifting the singlephase load as necessary. Supply voltages shouldbe evenly balanced as closely as can be read on acommercial voltmeter.A recent national survey by U.L. indicated that 36 out of83 utilities surveyed, or 43%, allowed voltage unbalancein excess of 3%, and 30% allowed voltage unbalanceof 5% or higher.In the event of a supply voltage unbalance, the powercompany should be notified of such unbalance todetermine if the situation can be corrected.Unless the unbalance can be corrected, the only wayto insure motor safety is to be sure the protectors aremounted in the high current phases when using two legprotection, or to use protectors in all three legs.A simple single phase condition in the load circuit willcause the current in two of the three phases to increase,while there will be no current in the open phase.A motor can be protected against this type of failurewith only two protectors, since there will always be atleast one protector in a line carrying the high singlephase current.© 1967 Emerson Climate Technologies, Inc.All rights reserved.10-11

The effect of an open phase in the primary circuit of apower transformer depends on the type of transformerconnection. Where both primary and secondary windingsare connected in the same fashion, wye-wye or deltadelta,a fault in one phase of the primary will result ina low current in one phase of the secondary, and highcurrents in two phases, with results similar to the simpleload circuit single phase condition.But in wye-delta or delta-wye connected powertransformers, an open circuit or single phase on theprimary side of the transformer will result in a high currentin only one phase of the motor with low currents in theother two phases.motor would still be protected should the high currentfall in either of the two protected legs. Therefore, thestatistical chances of failure are small, so normally nospecial provisions for this type of protection are providedunless required by code or regulatory bodies. However,if a primary single phase fault occurs, it may last forseveral hours, and motors not adequately protectedare quite likely to fail.Most of the three phase protections systems usedby Emerson Climate Technologies, Inc. will protectUnder locked rotor conditions, the high phase willdraw an amperage slightly less than nameplate lockedrotor current, while the other two legs will each drawapproximately 50% of that amount. Under operatingconditions, the current in the high phase could be inexcess of 200% of full load amperes, depending on load,while the current in the other two legs will be slightlygreater than normal full load amperes.Since the majority of power systems now use wye-deltaor delta-wye transformer connections, occasional faultsof this type can be expected.Most commercial power systems are quite reliable, and ifa primary single phase condition does occur in a systemwhere the compressor has only two leg protection, theagainst primary single phasing, but if there is anyquestion concerning an application, the matter shouldbe referred to the Emerson Climate Technologies, Inc.Application Engineering Department. However, whereunbalanced supply voltages and single phase loadsrepresent a continuing threat to three phase motor life,it is recommended that inherently protected motors beused, or if inherent protection is not available becauseof motor size, the motor-compressor should be equippedwith 3 leg protection.10-12© 1967 Emerson Climate Technologies, Inc.All rights reserved.

Section 11ACCESSORIESA number of accessory items are used in refrigerationcircuits for specific purposes, and their requirement ina particular system depends on the application.RECEIVERSA receiver is primarily a liquid storage tank for refrigerantwhich is not in circulation. Small package systemsutilizing capillary tubes for liquid refrigerant feed mayhave very small refrigerant charges, and if the operatingload is fairly constant, careful design of the evaporatorand condenser may allow the elimination of the receiverfrom the system. If the condenser has volume enoughto provide storage space, a separate receiver is notrequired, and this is common design practice in watercooledunits with shell and tube condensers. However,on practically all air cooled units equipped with expansionvalves, a separate receiver is required.In order to provide space to store the refrigerantcharge when maintenance is required on the system,the receiver should be large enough to hold the entirerefrigerant charge. A valve at the receiver outlet isrequired in order to pump the refrigerant charge intothe receiver, an operation commonly called pumpingthe system down.The outlet of the receiver must be so located that a liquidseal is maintained at the outlet even though the level inthe receiver tank may vary, to prevent any vapor fromentering the liquid line. Therefore if the outlet is at thetop, or if a side outlet is provided, a dip tube extendingto approximately ½” from the bottom of the receiver isused.gas flows through the large center tube, while liquid ispiped through the smaller tube wrapped around thesuction tubing. The cold suction vapor absorbs heatfrom the warm, high pressure liquid through the tubeto tube metal contact. Internal fins are often providedin the suction gas section to increase the heat transferbetween the suction gas and the liquid refrigerant.SUCTION ACCUMULATORSIf liquid refrigerant is allowed to flood through the systemand return to the compressor before being evaporated,it may cause damage to the compressor due to liquidslugging, loss of oil from the crankcase, or bearingwashout. To protect against this condition on systemsHEAT EXCHANGERSA heat exchanger is a device for transferring heat fromone medium to another. In commercial refrigerationsystems the general term of heat exchanger is usedto describe a component for transferring heat from theliquid refrigerant to the refrigerant suction gas.As mentioned previously, a heat exchanger is usedto raise the temperature of the return gas to preventfrosting or condensation, to subcool the liquid refrigerantsufficiently to prevent the formation of flash gas in theliquid line, to evaporate any liquid refrigerant floodingthrough the evaporator, and to increase systemcapacity.A typical heat exchanger is shown in Figure 61. Suction© 1967 Emerson Climate Technologies, Inc.All rights reserved.11-1

vulnerable to liquid damage such as heat pumps, truckrefrigeration, or on any installation where liquid floodbackcan occur, a suction accumulator is often used.The accumulator’s function is to intercept liquid refrigerantbefore it can reach the compressor crankcase. It shouldbe located in the compressor suction line between theevaporator and the compressor, should have a capacitylarge enough to hold the maximum amount of liquidthat might flood through, and must have provisionsfor a positive return of oil to the crankcase. Either asource of heat must be provided to evaporate the liquidrefrigerant or a means must be provided to meter theliquid to the compressor at a safe rate. A positive oilreturn must also be provided so that oil does not trapin the accumulator.Figure 62 illustrates a vertical accumulator with a U-tubesuction connection.Dehydrators or driers, as they are commonly called,consist of a shell filled with a desiccant or drying agent,with an adequate filter at each end. Some driers are madein porous block form so that the refrigerant is filtered bythe entire block. Driers are mounted in the refrigerantliquid line, so that all of the refrigerant in circulation mustpass through the drier each time it circulates throughthe system. Most driers are so constructed that they canserve a dual function as both filter and drier.Many different drying agents are used, but practicallyall modern driers are either of the throwaway type, orof the replaceable element type, and it is consideredgood practice to discard the used drier element eachtime the system is opened, and replace with a new drieror drier element.SUCTION LINE FILTERSOIL SEPARATORSAlthough well designed systems are effective inpreventing oil return problems, there are some caseswhere the use of oil separators may be necessary.They are most often required on ultra-low temperaturesystems, with flooded evaporators, or on other systemswhere inherent oil return problems are present.An oil separator is basically a separation chamber for oiland discharge gas. There is always some oil in circulationin a refrigeration system and oil leaving the compressoris entrained in the hot discharge gas which is travelingat high velocity. The oil separator when used is installedin the discharge line between the compressor and thecondenser. By means of baffles and a reduction of gasvelocity in the oil separator chamber, most of the oilis separated from the hot gas, and is returned to thecompressor crankcase by means of a float valve andconnecting tubing. The efficiency of an oil separatorvaries with load conditions, and is never 100% effectiveeven under ideal conditions. If system design causesoil logging, an oil separator may only delay lubricationdifficulty rather than cure it.DEHYDRATORSMoisture is one of the basic enemies of a refrigerationsystem, and the moisture level in an operating systemmust be held to an acceptable low level to avoid systemmalfunctions or compressor damage. Even with the bestprecautions, moisture will enter a system any time it isopened for field service. Unless the system is thoroughlyevacuated and recharged after exposure to moisture, theonly other effective means of removing small amountsof moisture is with a dehydrator.In order to protect the compressor from contaminationleft in the system at the time of installation, suctionline filters are widely used. The suction line filter isdesigned for permanent installation in the suction line,and may be of the sealed type, or may be equipped witha replaceable element so that the filter can be easilychanged if necessary.The replaceable element type is convenient for installinga system cleaning filter-drier element in the event ofsystem contamination.VIBRATION ELIMINATORSIn order to prevent the transmission of noise and vibrationfrom the compressor through the refrigeration piping,vibration eliminators are frequently installed in both thesuction and discharge lines. On small units, where smalldiameter soft copper tubing is used for the refrigerant11-2© 1967 Emerson Climate Technologies, Inc.All rights reserved.

lines, a coil of tubing may provide adequate protectionagainst vibration. On larger compressors, flexible metallichose is most frequently used.STRAINERSThe moisture indicator provides a warning signal forthe serviceman in the event moisture has entered thesystem, indicating that the dehydrator should be changedor that other action should be taken to effectively drythe system.DISCHARGE MUFFLERSStrainers, as the name implies, are mounted in refrigerantlines to strain any dirt, metal chips, etc. out of therefrigerant which might cause a malfunction in eitherthe refrigerant control devices or the compressor. Whilethe configuration of the strainer will vary, basically it iscomprised of a shell with a fine mesh screen. Becauseof the small orifice in expansion and solenoid valves,strainers are normally mounted just upstream from themin the refrigerant liquid line.SIGHT GLASS AND MOISTURE INDICATORSA sight glass in the liquid line allows the operator orserviceman to observe the flow of liquid refrigerant.Bubbles or foaming in the sight glass indicate a shortageof refrigerant, or a restriction in the liquid line that isadversely affecting system operation. Sight glasses arewidely used as a means of determining if the system isadequately charged when adding refrigerant.Moisture indicators have been incorporated in sightglasses as shown in Figure 65.On systems where noise transmission must be reduced toa minimum, or where compressor pulsation might createvibration problems, a discharge muffler is frequently usedto dampen and reduce compressor discharge noise.The muffler is basically a shell with baffle plates, withthe internal volume required primarily dependent onthe compressor displacement, although the frequencyand intensity of the sound waves are also factors inmuffler design.CRANKCASE HEATERSWhen the compressor is installed in a location whereit will be exposed to ambient temperatures colder thanthe evaporator, refrigerant migration to the crankcasecan be aggravated by the resulting pressure differencebetween the evaporator and compressor during offcycles. To protect against the possibility of migration,crankcase heaters are often employed to keep the oil inthe crankcase at a temperature high enough so that anyliquid refrigerant entering the crankcase will evaporateand create a pressure sufficient to prevent large scalemigration.Crankcase heaters may be of the insert type or can bemounted externally on the crankcase. The heater is alow wattage resistance element, normally energizedcontinuously, and must be carefully selected to avoidoverheating of the oil in the compressor.© 1967 Emerson Climate Technologies, Inc.All rights reserved.11-3

REFRIGERATION GAUGESPressure gauges, especially calibrated for refrigerationusage, are the primary tool of the serviceman in checkingsystem performance. Gauges for the high pressure sideof the system have scales reading from 0 psig to 300psig (or for usage on higher pressures, from 0 psig to 400psig). Gauges for the low pressure part of the system aretermed compound gauges, since the scale is graduatedfor pressures above atmospheric pressure in psig, andfor pressures below atmospheric pressure in vacuum ininches of mercury. The compound gauge is calibratedfrom 30 inches of vacuum to pressures ranging from 60psig to 150 psig depending on gauge design.In addition to the pressure scales, equivalent saturationtemperatures for commonly used refrigerants are usuallyshown on the gauge dial.11-4© 1967 Emerson Climate Technologies, Inc.All rights reserved.

© 1967 Emerson Climate Technologies, Inc.All rights reserved.

© 1967 Emerson Climate Technologies, Inc.All rights reserved.

Form No. AE 102 R2 (10/06))Emerson®, Emerson. Consider It Solved, Emerson Climate Technologies andthe Emerson Climate Technologies logo are the trademarks and service marks ofEmerson Electric Co. and are used with the permission of Emerson Electric Co.Copelametic®, Copeland®, and the Copeland® brand products logo are thetrademarks and service marks of Emerson Climate Technologies, Inc.All other trademarks are the property of their respective owners.Printed in the USA. © 1967 Emerson Climate Technologies, Inc. All rights reserved.1675 W. Campbell Rd.Sidney, OH 45365EmersonClimate.com