GF - A 4
Furnace Sequences Of Operation
24VAC Mode
1. This furnace modulates between 40% and 100% of capacity,
in 3% increments, every 1 minute. The furnace always lights at
approximately 65% and will modulate up or down; depending
on the 24VAC thermostat signal. Requested capacity can be
seen in the “STATUS” section of the User Interface menu.
2. R and W1 contacts close signaling the control board
(IFC) to run its self-check routine. After the control has
verified that all safeties are closed and PS1, PS2,
and PS3 pressure switch contacts are open, the IFC
signals the variable speed inducer drive to start the vent
motor at the speed needed to close pressure switches PS1
and PS2.
3. PS1 and PS2 close.
4. The IFC receives a 24 VAC signal from PS1 and PS2
when they close. This verifies the vent motor is moving
the correct amount of combustion air through the furnace and
the vent system.
5. IFC starts the hot surface ignitor learning routine
warm-up time cycle.
6. IFC turns on the gas valve. Trial time for ignition is 5
seconds.
7. The IFC verifies ignition by the flame current sensing method.
If a flame is not detected, the IFC will cycle the furnace three
times to try and verify a flame. If no flame is detected, the IFC
will lockout for one hour. The IFC will send an alert code to the
User Interface as well as flash its Red alert LED two times
repeatedly.
8. If a flame is detected, the IFC will start the heat exchanger
warm-up time delay for the indoor blower.
9. “IGNITION” will now be displayed in the “STATUS” section of
the User Interface menu.
Note:
Pressure Switch 1 closes at approximately 40% of capacity.
Pressure Switch 2 closes at approximately 65% of capacity.
Pressure Switch 3 closes at approximately 95% of capacity.
Thermostat call for W1 (2 stage heating thermostat)
Note:
The furnace lights at approximately 65% of capacity.
10. After 45 seconds, the IFC signals the indoor blower motor
to run at the programmed ignition sequence speed.
11. The IFC then signals the variable speed inducer motor
drive board to ramp down to the corresponding speed to
keep PS1 closed. The reduction of the vent motor speed
in steps allows the gas flow through the gas valve to also be
reduced in steps, decreasing the chance of burner flame out.
The W1 heating capacity is 40%. The IFC will also decrease
the indoor blower motor speed.
Thermostat call for W2 after W1
12. R and W2 thermostat contacts close signaling a call
for W2 heat. The IFC then signals the variable speed inducer
drive to ramp up the vent motor allowing flow through
the gas valve to also be increased in 3% steps.
13. If the call for W2 remains, this 3% increase will be repeated
every 1 minute until the capacity requested is 100%. The IFC
will also increase the indoor blower motor speed in
appropriate steps.
W2 satisfied, W1 still called for
14. R and W2 thermostat contacts open signaling that
W2 heating requirements have been satisfied. The IFC will
signal the variable speed vent motor to slow down to its
learned W1 speed. The gas valve will reduce the gas flow to
40% capacity and the indoor blower motor speed will be reduced.
W1 satisfied
15. R and W1 thermostat contacts open signaling that
W1 heating requirements have been satisfied. The gas valve
will be de-energized and gas flow will cease. The variable
speed vent motor will de-energize approximately after a 5
second post purge. The indoor blower motor will be de-
energized after the fan off delay period has ended. (The indoor
blower heat fan off delay is field selectable and can be adjusted
using the User Interface menu. It is factory set at 100
seconds but can be set to 60, 140, or 180 seconds
Thermostat call for heat (1 stage heating thermostat)
16. W1 and W2 must be jumpered at the IFC. R and
W1 contacts close signaling the control board (IFC) to run its
self- check routine. After the control has verified that all safeties
are closed and PS1, PS2, and PS3 pressure switch
contacts are open, the IFC signals the variable speed inducer
drive to start the vent motor at the speed needed to close
pressure switches PS1 and PS2.
17. PS1 and PS2 close.
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24 VAC Mode
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