SYSTEM OPERATION
8
When the thermostat is satisfied, breaking the circuit
between R to Y and R to G, the compressor and outdoor
fan motor will stop. The indoor blower will stop after a
programmed 60 second off delay.
NOTE: Should the second stage heating contacts in
the room thermostat close, a W1 signal will be sent to
the ignition control and the Y signal would be removed.
A normal gas heating sequence would then follow.
Ignition Control Sequence Of Operation
A. Heating Operation: Low stage heat
1. Thermostat type is set to two-stage.
2. Thermostat “W1” input initiates low stage heating.
3. Induced draft blower is energized at high speed for
the pre-purge period. Pre-purge timer begins after
control recognizes pressure switch has closed.
4. Trial-for-ignition period begins after pre-purge
period expires. Low and high stage gas valves are
energized along with the igniter for trial-for-ignition
period. Igniter is de-energized when flame is
detected.
5. Flame is achieved and detected during trial-for-
ignition period. Flame stabilization period begins
when flame is detected.
6. De-energize high stage gas valve and switch induced
draft blower to low speed within five seconds of flame
detection.
7. Air circulating blower is energized at low heat speed
after heat ON delay time expires. Heat ON delay
timer begins when flame is detected.
8.
Control monitors thermostat, flame, limit, and
pressure switch inputs during low stage heating.
9. Thermostat “W1” input is removed.
10. Low stage gas valve is de-energized.
11. Induced draft blower remains energized at low speed
for post purge period.
12. Air circulating blower remains energized at low heat
speed for heat OFF delay. Heat OFF delay begins
when “W1” input is removed.
13. Control returns to Standby and awaits next
thermostat request.
B. Heating Operation: High stage heat
1. Thermostat type is set to two-stage.
2. Thermostat “W1” and “W2” inputs initiate high stage
heating.
3. Induced draft blower is energized at high speed for
the pre-purge period. Pre-purge timer begins after
control recognizes pressure switch has closed.
4. Trial-for-ignition period begins after pre-purge
period expires. Low and high stage gas valves are
energized along with the igniter for trial-for-ignition
period. Igniter is de-energized when flame is
detected.
5. Flame is achieved and detected during trial-for-
ignition period. Flame stabilization period begins
when flame is detected.
6. Gas valve and induced draft blower remain at high
stage and high speed.
7. Air circulating blower is energized at high heat speed
after heat ON delay time expires. Heat ON delay
timer begins when flame is detected.
8.
Control monitors thermostat, flame, limit, and
pressure switch inputs during high stage heating.
9. Thermostat “W1” and “W2” inputs are removed.
10. High and low stage gas valves are de-energized.
11. Induced draft blower switches from high speed to low
speed and remains energized for post purge period.
12. Air circulating blower remains energized at high heat
speed for High Stage Heat OFF Delay period then
switches to low heat speed for the remainder of the
selected heat OFF delay. Heat OFF delay begins
when “W1” and “W2” inputs are removed.
13. Control returns to Standby and awaits next
thermostat request.
A. Cooling Operation: Low stage cool
1. Thermostat type is set to two-stage.
2. Thermostat “Y1” or thermostat “Y1” and “G” input
initiates low stage cooling.
3. IDT/ODT/Pressure/Loss of Charge Switch circuits
are checked for closed condition. Cooling operation
can proceed only if these circuits are closed.
4. Low stage compressor output is energized.
5. Condenser fan motor is energized at low speed.
6. Air circulating blower is energized at low cool speed
after cool ON delay expires. Cool ON delay timer
begins when thermostat inputs are detected.
7.
Control monitors thermostat, gas valve, flame, and
IDT/ODT/Pressure/Loss of Charge Switches during
low stage cooling.
8. Thermostat “Y1” or “Y1” and “G” inputs are removed.
9. Low stage compressor output is de-energized. Low
speed condenser fan motor is de-energized.
10. Air circulating blower remains energized at low cool
speed for the cool OFF delay. Cool OFF delay timer
begins when thermostat input is removed.
11. Control returns to Standby and awaits next
thermostat request.
B. Cooling Operation: High stage cool
Thermostat type is set to two-stage.
Thermostat “Y1” and “Y2” or “Y1”, “Y2” and “G” inputs
initiate high stage cooling.
IDT/ODT/Pressure/Loss of Charge Switch circuits are
checked for closed condition. Cooling operation can
proceed only if these circuits are closed.
