Installation Operation Maintenance

OperationUnoccupied modeIf the thermostat being used isprogrammable, it will have its ownstrategy for unoccupied mode andwill control the unit directly. If amechanical thermostat is beingused, a field applied time clock withrelay contacts connected to J6-11and J6-12 can initiate anunoccupied mode as follows:• Contacts open: Normal occupiedoperation.• Contacts closed: Unoccupiedoperation as follows - Fan inauto mode regardless of fanswitch position. Economizercloses except while economizingregardless of minimum positionsetting.Cooling/Economizer OperationIf unit does not have an economizer,the Cool/Econ Stage 1 and Stage 2will call directly for mechanicalcooling (compressor) stages. If theunit has an economizer, theCool/Econ stages will function asshown in Table 46.Setting the economizer or0-50% motorized hood(option)The ECA board is mounted on thedamper actuator. To access the ECAboard on economizers:• Remove the filter access panel ofthe unit.• The electrical power must bedisconnected to set theminimum position and check theeconomizer.• Disconnect the power supply,put the thermostat fan selectorto "ON" and the "HEAT/COOL"selector to "OFF". This puts thedamper in the minimumventilation position.• To set the required minimumventilation air position, turn thedial on the ECA clockwise toincrease ventilation, or anticlockwiseto decrease ventilation.The damper will open at thissetting whenever the fan circuitis powered up (see Figure 25).• When the arrow on the dial'sadjustment screw is pointing to8 o'clock, the minimum positionis roughly 0%. When the dial ispointing to 12 o'clock it isroughly 25%, and when the dialis pointing to 4 o'clock it isroughly 50% (see figure 25).Table 46 - Cooling/Economizer Operation with ThermostatOK toEconomize?ThermostatY1ThermostatY2Call for EconomizerCoolingCompressor StagingRequestNo On Off Inactive Compressor Output 1No Off On Inactive Compressor Output 2No On On InactiveCompressorOutputs 1 & 2Yes On Off Active OffYes Off On Active Compressor offYes On On Active CompessorNotes:40 to 50 ton CV onlyThis unit has 3 stages of cooling if using a zone sensor. If using a conventional thermostat it has 2 stages asfollows:Y1 = 1st stageY1 + Y2 = 3rd stageVAVThermostat inputs are ignored on VAV units.50RT-SVX20B-E4