GF - A 2
Furnace Sequences Of Operation
16
Communication Mode
1. This furnace is fully modulating between 40% and
100% of capacity in .6% increments. The furnace
always lights at approximately 65% and will modulate
up or down; depending on the communicating comfort
control demand. Requested capacity can be seen in
the “STATUS” section of the User Interface menu.
2. The communicating comfort control signals the
furnace IFC for heat.
3. The IFC then checks all safeties, thermostats,
and pressure switches PS1, PS2, and
PS3.
4. The IFC signals the variable speed inducer drive
to start the vent motor at the speed needed to
close pressure switches PS1 and PS2.
5. PS1 and PS2 close.
6. 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 com-
bustion air through the furnace and the vent system.
7. IFC starts the hot surface ignitor learning
routine warm-up time cycle.
8. IFC turns on the gas valve. Trial time for
ignition is 5 seconds.
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.
Note:
The furnace lights at approximately 65% of capacity.
9. 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
communicating comfort control and User Interface.
The Red alert LED flashes two times repeatedly.
10. If a flame is detected, the IFC will start the heat
exchanger warm-up time delay for the indoor blower.
11. “IGNITION” will now be displayed in the “STATUS”
section of the User Interface menu.
12. After 45 seconds, the IFC signals the indoor
blower motor and run at the programmed ignition
sequence speed.
13. Depending on the communicating comfort control
demand, the IFC will then signal the variable
speed inducer motor drive board and the indoor
blower motor to ramp up or down.
14. With a heat demand less than 65% from the
communicating comfort control, the IFC signals
the variable speed inducer motor drive board to
ramp down to that corresponding demand speed. 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 minimum capacity change is 1%.
15. The minimum capacity of all furnaces is 40%,
with the exception of the *UHMC120. The minimum
capacity for this furnace is 45%.
16. The communicating comfort control will continue
to call for the requested capacity demand until the
indoor temperature is back at the set point OR,
17. If the communicating comfort control does not
detect that the indoor temperature is moving back
towards its set point or the indoor temperature is still
moving away from the set point, it will signal the IFC
to go to a higher capacity of heat.
1
2
3
7
8
9
4a
4b 4c 4d
1
3
2
8
Communication Mode
5a 5b
5c
5a 5b
5a
5b
3
5a
5b
6b
6b
3
3
2
3
1
10
3
10
3
6a
6a
6b
2
6a
3
2
2
3
To Next Page
Loading...
