OPERATING SEQUENCE
Cooling, Units Without Economizer Ð When thermostat calls for cooling, terminals G and Y1 are energized. The indoor (evaporator) fan contactor (IFC) and compressor contactor no. 1 (C1) are energized, and evaporator-fan motor (IFM), com- pressor no. 1 (580D036-150 and 579F216-300) or unloaded compressor (579F180), and condenser fan(s) start. The liquid line solenoid value for compressor no. 1 is deenergized open. The condenser-fan motor(s) runs continuously while unit is cool- ing. For units with 2 stages of cooling, if the thermostat calls for a second stage of cooling by energizing Y2, compressor con- tactor no. 2 (C2) is energized and compressor no. 2 starts (580D090-150 and 579F216-300), or compressor no. 1 runs fully loaded (579F180). The liquid line solenoid valve for com- pressor no. 2 (579F180 and 240) is deenergized to open.
Heating, Units Without Economizer (580D036-150) Ð When the thermostat calls for heating, terminal W1 is energized. In or- der 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 (IDM) is then energized and the burner ignition sequence begins. The indoor (evaporator) fan motor (IFM) is energized 45 seconds after a ¯ame is ignited. 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 energized. When the thermostat is satis®ed and W1 is deenergized, the IFM stops after a 45-second time- off delay.
Heating, Units Without Economizer (579F180-300)
NOTE: The 579F180-300 units have 2 stages of heat.
When the thermostat calls for heating, power is sent to W on the IGC (integrated gas unit controller) board. An LED (light- emitting diode) on the IGC board will be on during normal op- eration. A check is made to ensure that the rollout switch and limit switch are closed. The induced-draft motor is then ener- gized, and when speed is proven with the hall effect sensor on the motor, the ignition activation period begins. The burners will ignite within 5 seconds.
If the burners do not light, there is a 22-second delay before an- other 5-second attempt. If the burners still do not light, this se- quence is repeated for 15 minutes. After the 15 minutes have elapsed, if the burners still have not lighted, heating is locked out. To reset the control, break 24-v power to the thermostat.
When ignition occurs the IGC board will continue to monitor the condition of the rollout and limit switches, the hall effect sensor, as well as the ¯ame sensor. If the unit is controlled through a room thermostat set for fan auto., 45 seconds after ignition oc- curs, the indoor-fan motor will be energized. If for some reason the overtemperature limit opens prior to the start of the indoor fan blower, on the next attempt, the 45-second delay will be shortened to 5 seconds less than the time from initiation of heat to when the limit tripped. Gas will not be interrupted to the burn- ers and heating will continue. Once modi®ed, the fan on delay will not change back to 45 seconds unless power is reset to the control.
When additional heat is required, W2 closes and initiates power to the second stage of the main gas valve. When the thermostat is satis®ed, W1 and W2 open and the gas valve closes, inter- rupting the ¯ow of gas to the main burners. If the call for W1 lasted less than 1 minute, the heating cycle will not terminate until 1 minute after W1 became active. If the unit is controlled through a room thermostat set for fan auto., the indoor-fan mo- tor will continue to operate for an additional 45 seconds then stop. If the overtemperature limit opens after the indoor motor is stopped within 10 minutes of W1 becoming inactive, on the next cycle the time will be extended by 15 seconds. The maximum delay is 3 minutes. Once modi®ed, the fan off delay will not change back to 45 seconds unless power is reset to the control.
A LED indicator is provided on the IGC to monitor operation. The IGC is located by removing the side panel and viewing the IGC through the view port located in the control box access panel. During normal operation, the LED is continuously on.
Cooling, Units With Durablade Economizer (580D036-150)
ÐWhen the outdoor-air temperature is above the OAT (outdoor-air thermostat) setting and the room thermostat calls for cooling, compressor contactor no. 1 is energized to start compressor no. 1 and the outdoor (condenser) fan motor (OFM). The indoor (evaporator) fan motor (IFM) is energized and the economizer damper moves to the minimum position. Upon a further call for cooling, compressor contactor no. 2 will be energized, starting compressor no. 2 (090-150 only). After the thermostat is satis®ed, the damper moves to the fully closed position when using an auto fan or to the minimum position when using a continuous fan.
When the outdoor-air temperature is below the OAT setting and the thermostat calls for cooling, the economizer dampers move to the minimum position. If the supply-air temperature is above 57 F, the damper continues to open until it reaches the fully open position or until the supply-air temperature drops below 52 F.
When the supply-air temperature falls to between 57 F and 52 F, the damper will remain at an intermediate open position. If the supply-air temperature falls below 52 F, the damper will modulate closed until it reaches the minimum position or until the supply-air temperature is above 52 F. When the thermostat is satis®ed, the damper will move to the fully closed position when using an auto fan or to the minimum position when using a continuous fan.
If the outdoor air alone cannot satisfy the cooling requirements of the conditioned space, economizer cooling is integrated with mechanical cooling, providing second-stage cooling. Compres- sor no. 1 and the condenser fan will be energized and the po- sition of the economizer damper will be determined by the supply-air temperature. Compressor no. 2 is locked out.
When the second stage of cooling is satis®ed, the compressor and OFM will be deenergized. The damper position will be de- termined by the supply-air temperature.
After a 30-second delay, the IFM shuts off. If the thermostat fan selector switch is in the ON position, the IFM will run continuously.
