Cooling, Units With Parablade Economizer (580D036-072)
ÐWhen the outdoor air is above the enthalpy control (EC) set- ting, and the room thermostat calls for cooling, and the com- pressor contactor is energized to start the compressor and the condenser-fan motor. The evaporator-fan motor is energized and the economizer damper moves to the minimum position. Af- ter the room thermostat is satis®ed, the damper will spring re- turn to the fully closed position.
When the outdoor air is below the (EC) setting and the ther- mostat calls for cooling, the economizer outdoor-air damper is opened proportionally to maintain between 50 and 56 F at the mixed-air sensor. If outdoor air alone cannot satisfy the cooling requirements, economizer cooling is integrated with mechanical cooling. When the room thermostat is satis®ed, the damper will spring return to the fully closed position.
Cooling, Units With Parablade Economizer (580D090-150)
ÐWhen the outdoor air is above the enthalpy control (EC) set- ting, and the room thermostat calls for cooling, and compressor contactor no. 1 is energized to start compressor no. 1 and the condenser-fan motor. The evaporator-fan motor is energized and the economizer damper moves to the minimum position. Upon a further call for cooling, compressor contactor no. 2 is en- ergized, starting compressor no. 2. After the room thermostat is satis®ed, the damper will spring return to the fully closed position.
When the outdoor-air temperature is below the EC setting and the thermostat calls for cooling, the economizer outdoor-air damper is opened proportionally to maintain between 50 and 56 F at the mixed-air sensor. If outdoor-air alone cannot satisfy the cooling requirements, economizer cooling is integrated with mechanical cooling, and the second compressor is locked out.
When the room thermostat is satis®ed, the damper will spring return to the fully closed position.
Cooling, Units With Economizer (579F180-300) Ð Upon a call for cooling, when outdoor ambient is above the temperature control setting, the economizer damper moves to VENT posi- tion. The compressors and evaporator and condenser fans energize.
Upon a ®rst call for cooling, when outdoor ambient is below the temperature control setting, the evaporator fan starts and the economizer opens to maintain 53 F leaving-air temperature. The compressors remain off.
Upon a second-stage call for cooling, compressor no. 1 is en- ergized and mechanical cooling is integrated with econo- mizer cooling. If the outdoor-air temperature drops below 50 F, a cooling lockout switch prevents the compressors from running.
When supply-air temperature drops below a ®xed set point, the economizer damper modulates to maintain the temperature at the ®xed set point.
A freeze protection thermostat (FPT) is located on the evapora- tor coil. It detects frost build-up and turns off the compressors, allowing the coil to clear. Once frost has melted, the compres- sors can be reenergized.
Heating, Units With Economizer (580D036-150) Ð When the thermostat calls for heating, terminal W1 is energized. In order to prevent thermostat short-cycling, the unit is locked into the Heating mode for at least 1 minute when W1 is energized. The induced-draft motor is then energized and the burner ignition sequence begins. The indoor (evaporator) fan motor (IFM) is energized 45 seconds after a ¯ame is ignited and the damper moves to the minimum position. On units equipped for two stages of heat, when additional heat is needed, W2 is energized and the high-®re solenoid on the main gas valve (MGV) is en- ergized. When the thermostat is satis®ed and W1 is deener- gized, the IFM stops after a 45 second time-off delay. The economizer damper then moves to the fully closed position. When using continuous fan, the damper will remain in the mini- mum position.
Heating, Units With Economizer (579F180-300) Ð Outdoor- air damper stays at VENT position while evaporator fan is op- erating. Refer to Heating, units without economizer section on page 63 for remainder of operating sequence.
