GF - A 14
Furnace Sequences Of Operation
UD2 Communicating Mode
Comfort control call for 1st stage heat ((A/T)CONT900)
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
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 after 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
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 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
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 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 “CONTINUOUS”
The comfort control signals a continuous fan call. The
continuous fan cfm is field selectable and can be adjusted
through the User Interface menu. The factory setting is 50%
of the cooling cfm selected but can be set at 25%, 50%, 75%,
or 100%. If the system has a 2 stage outdoor unit, the setting is
50% of the 2nd stage cooling cfm.
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.
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UD2 Communicating Mode
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