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SEQUENCE OF OPERATION
Heating Cycle
During a call for heat, the thermostat closes R - W circuit of the
control board. The control board verifies limit switches are closed
and pressure switch is open. The induced draft blower relay
closes, causing the blower to run. As vent pressure is developed
by the induced draft blower, the pressure switch closes. After a
15-second pre-purge, the control energizes the hot surface
igniter. After a 7-second warm-up time, the control energizes the
main gas valve, causing the main burners to ignite. The hot
surface igniter is de-energized 3 seconds after the main valve
opens. If flame is sensed during this time, the main valve remains
energized and the control starts the 30-second heat blower “on”
delay.
As heating demand is met, the thermostat de-energizes the R - W
circuit. The control de-energizes the main valve, causing the
burners to shut off. The induced draft blower shuts off after a
15-second post-purge delay. The circulating air blower will
continue to operate until the user-selectable heat blower “off”
delay expires. The control returns to standby mode once the heat
blower “off” delay expires.
Fan On Cycle
During a fan on call, the thermostat energizes the R - G circuit of
the control board, immediately causing the fan to energize the
COOL speed. The fan remains energized as long as the
thermostat calls for fan on operation.
If a call for cooling is energized during a fan on call, the fan
continues to operate at the COOL speed. If a call for heat is
energized during a fan on call, the control de-energizes the fan
immediately and begins the heat call/ignition sequence.
At the end of the fan on call, the thermostat de-energizes the
R - G circuit of the control, causing the fan to be de-energized
immediately.
Cooling Cycle
During a call for cooling, the thermostat energizes the R - Y
circuit of the control board. After a 1-second cooling “on” delay,
the control energizes the cooling fan speed. If the fan is already
energized, it remains running and does not de-energize for the
1-second cooling fan “on” delay.
The call for cooling has priority over continuous fan operation
while a call for heating has priority over both a call for cooling or
continuous fan. Ignition lockouts for any reason do not affect
cooling operation.
As cooling demand is met, the thermostat de-energizes the R - Y
circuit of the control board. After a 60-second cooling “off” delay,
the control de-energizes the cooling speed fan. At the end of the
cooling “off” delay period, the control returns to the standby
mode.
