GF - A 16
Furnace Sequences Of Operation
UD2 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 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.
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
approximately 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 approximately
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 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 2nd stage speed heating airflow. At
the same time, the 2nd stage draft inducer is energized and
the 2nd stage pressure switch then closes. The 2nd stage
gas valve is then energized. (The inter-stage delay is field
selectable and can be adjusted through the User Interface
menu. It is factory 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.
Thermostat satisfied
R and W / (jumpered on IFC) thermostat contacts open
signaling the heating requirements have been satisfied. The gas
valve is de-energized and after a 5 second draft inducer post
purge, the draft inducer is de-energized. If the inter-stage delay
was met and the furnace was operating on 2nd stage heat, the
indoor motor will operate at 2nd stage heating airflow for the
duration of the 2nd stage heating fan off delay.
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UD2 24v Mode
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