vector 1800 mt - Sunbelt Transport Refrigeration

2.16 REFRIGERANT CIRCUIT DURING COOLING (See Figure 2-11 thru Figure 2-14)When cooling, the unit operates as a vapor compressionrefrigeration system. The main components of thesystem are: the (1) reciprocating compressor, (2)air-cooled condenser, (3) electronic expansion valve,and (4) direct expansion evaporator.The compressor raises the pressure and thetemperature of the refrigerant and forces it into thecondenser tubes. The condenser fan circulatessurrounding air over the outside of the condenser tubes.The tubes have fins designed to improve the transfer ofheat from the refrigerant gas to the air. This removal ofheat causes the refrigerant to liquify. Liquid refrigerantleaves the condenser and flows to the receiver.The receiver stores the additional charge necessary forlow ambient operation. The receiver is equipped with arelief valve (See Section 2.12)The refrigerant leaves the receiver and flows throughthe manual shut off valve (King valve) to the subcooler.The subcooler occupies a portion of the maincondensing coil surface and gives off further heat to thepassing air.The refrigerant then flows through a filter-drier where anabsorbent keeps the refrigerant clean and dry.The refrigerant flows to the “Liquid/suction” heatexchanger. Here the liquid is further reduced intemperature by giving off some of its heat to the suctiongas.The liquid then flows to an externally equalizedelectronic expansion valve (EVXV) which reduces thepressure of the liquid and meters the flow of liquidrefrigerant to the evaporator to obtain maximum use ofthe evaporator heat transfer surface.The refrigerant pressure drop caused by the expansionvalve is accompanied by a drop in temperature so thelow pressure, low temperature fluid that flows into theevaporator tubes is colder than the air that is circulatedover the evaporator tubes by the evaporator fan. Theevaporator tubes have aluminum fins to increase heattransfer; therefore heat is removed from the aircirculated over the evaporator. This cold air is circulatedthroughout the box to maintain the cargo at the desiredtemperature.The transfer of heat from the air to the low temperatureliquid refrigerant causes the liquid to vaporize.This low temperature, low pressure vapor passesthrough the evaporator outlet temperature and pressuresensors (EVOT and EVOP) which aid in calculation ofsuperheat. The vapor then passes through the “suctionline/liquid line” heat exchanger where it absorbs moreheat from the high pressure/high temperature liquid andthen returns to the compressor through the compressorsuction modulation valve (CSMV). The CSMV controlsthe compressor suction pressure thereby matching thecompressor capacity to the load.The remote evaporators are equipped with liquidsolenoid valves which open or close depending on thethermostat, and are also equipped with externallyequalized thermostatic expansion valves (TXV).2.17 REFRIGERANT CIRCUIT - HEATING AND DEFROSTING (See Figure 2-12 thru Figure 2-15)Compressor is turned off for all heating and defrostcycles. Heating is always accomplished using electricresistance heaters. Defrost may be accomplished usingeither electric heaters or return air. See Section 4.4.10for more information on heating and defrost.62-110392--24