44 18-CD30D1-12
Installer’s Guide
SEQUENCE 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.
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)
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.
Note:
The furnace lights at approximately 65% of capacity
.
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 communicating
comfort control (ERR 22) and User Interface (RETRY
LO) 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.
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)
Note: The inter-stage delay is field selectable and can
be adjusted through the User interface menu. It is fac-
tory set at 0 minutes but can be adjusted to 5, 10, or
15 minutes. This option can help optimize the furnace
to try to satisfy the heating requirement during low
heating load conditions.
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.
Note:
The furnace lights at approximately 65% of capacity
.
17. PS1 and PS2 close.
18. 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.
19. IFC starts the hot surface ignitor learning routine
warm-up time cycle.
20. IFC turns on the gas valve. Trial time for ignition is 5
seconds.
21. The IFC verifies ignition by the flame current sensing
method. If a flame is not detected, the IFC will cycle
