18-CD32D1-3
29
Installer’s Guide
SEQUENCE OF OPERATION
(Communicating Mode)
Comfort control call for 1st stage heat (A/TCONT900):
The comfort control signals the control board (IFC) to run
its self-check routine. After the control has verified that
all safeties are closed and the 1st stage pressure switch con-
tacts are open, the draft inducer will be energized on high
speed. After the draft inducer comes up to speed, the 1st
stage pressure switch contacts will close, the draft inducer
switches to low speed, and the igniter warm-up period will
begin. The igniter will heat for approximately 20 seconds;
the 1st stage gas valve will be energized to permit gas flow
to the burners. The flame sensor confirms that ignition has
been achieved within the 4 second ignition trial period.
As the flame sensor confirms that ignition has been
achieved, the delay to fan ON period begins timing and af-
ter approximately 45 seconds the indoor blower motor will
be energized at the 1st stage speed and will continue to run
during the heating cycle.
Comfort control call for 2nd stage after 1st stage:
The comfort control signals a call for 2nd stage heat. After a
30 second delay, the draft inducer will be energized on high
speed. The 2nd stage pressure contacts will close allowing
the 2nd stage gas valve to be energized. The indoor blower
motor will ramp up to 2nd stage heating airflow.
2nd stage satisfied, 1st stage still called for:
The comfort control signals that 2nd stage heating re-
quirements have been satisfied. The draft inducer motor
is reduced to low speed allowing the 2nd stage pressure
switch to open. The 2nd stage gas valve is de-energized
allowing 1st stage heating operation. After approximately
30 seconds, the indoor blower motor is reduced to 1st stage
heating airflow.
1st stage satisfied:
The comfort control signals that the 1st stage heating re-
quirements have been satisfied. The 1st stage gas valve will
be de-energized and gas flow will cease. The draft inducer
motor will be de-energized 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)
Indoor Blower motor operation thermostat fan
switch “ON” (Communicating Mode)
The communicating comfort control signals a continuous
fan call. The factory setting is 50% of the cooling cfm se-
lected but can be adjusted from 25% - 100% through the In-
staller Setup menu on the communicating comfort control.
If the outdoor unit is a 2 stage system, the factory setting is
50% of the 2nd stage cooling cfm. If the outdoor unit is a 24
volt single stage cooling system, the factory setting is 50%
of the cooling cfm.
NOTE: If the actual relative humidity (RH) is at or below
the set-point, the fan will run until the continuous fan call
is removed or the actual RH exceeds the set-point. If the
actual RH is above the set-point, the fan will not turn on.
See the communicating comfort control Installer’s Guide for
additional information.
Indoor Blower Timing:
The furnace control module (IFC) controls the variable
speed motor in the heating mode. The fan “ON” time is set
at 45 seconds and is not field selectable. The blower “OFF”
delay is factory set at 100 seconds and can be adjusted to
60, 140, or 180 seconds.
(24v Mode)
Thermostat call for 1st stage heat (2 stage heating
thermostat):
R and W1 thermostats contacts close signaling the control
board (IFC) to run its self-check routine. After the control
has verified that all safeties are closed and the 1st stage
pressure switch contacts are open, the draft inducer will be
energized on high speed.
After the draft inducer comes up to speed, the 1st stage
pressure switch contacts will close, the draft inducer
switches to low speed, and the igniter warm-up period will
begin. The igniter will heat for approximately 20 seconds;
the 1st stage gas valve will be energized to permit gas flow
to the burners. The flame sensor confirms that ignition has
been achieved within the 4 second ignition trial period.
As the flame sensor confirms that ignition has been
achieved, the delay to fan ON period begins timing and af-
ter approximately 45 seconds the indoor blower motor will
be energized at the 1st stage speed and will continue to run
during the heating cycle.
Thermostat call for 2nd stage after 1st stage:
R and W2 thermostat contacts close signaling a call for 2nd
stage heat. After a 30 second delay, the draft inducer will be
energized on high speed. The 2nd stage pressure contacts
will close allowing the 2nd stage gas valve to be energized.
The indoor blower motor will ramp up to 2nd stage heating
airflow.
2nd stage satisfied, 1st stage still called for:
R and W2 thermostat contacts open signaling that 2nd
stage heating requirements have been satisfied. The draft
inducer motor is reduced to low speed allowing the 2nd
stage pressure switch to open. The 2nd stage gas valve is
de-energized allowing 1st stage heating operation. After ap-
proximately 30 seconds, the indoor blower motor is reduced
to 1st stage heating airflow.
1st stage satisfied:
R and W1 thermostat contacts open signaling that the 1st
stage heating requirements have been satisfied. The 1st
stage gas valve will be de-energized and gas flow will cease.
The draft inducer motor will be de-energized after approxi-
mately 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)
W1 and W2 must be jumpered at the control board.
R and W thermostat contacts close signaling a call for heat.
The control board (IFC) runs it self check routine. After the
control has verified that all safeties are closed and the 1st
stage pressure switch contacts are open, the draft inducer
will be energized on high speed. After the draft inducer
comes up to speed, the 1st stage pressure switch contacts
will close, the draft inducer switches to low speed, and the
igniter warm-up period will begin. The igniter will heat for
approximately 20 seconds; the 1st stage gas valve will be
energized to permit gas flow to the burners. The flame sen-
sor confirms that ignition has been achieved within the 4
second ignition trial period.
As the flame sensor confirms that ignition has been
achieved, the delay to fan ON period begins timing and af-
ter approximately 45 seconds the indoor blower motor will
be energized at the 2nd stage speed heating airflow.
