GF - A 22
Furnace Sequences Of Operation
*UH3 Inducer Learning Routine Sequence
The furnace IFC will go through an inducer learning routine
for each stage of heat.
The learning routine is done to determine the correct amount of
ventilation air for complete combustion.
The inducer motor speed for each stage may be different for
each installation due to the different length and size of the
ventilation pipe, vent pipe, number of pipe fittings used, and the
type of vent cap installed.
The inducer learning routine is repeated each time the furnace IFC
is powered up and the furnace IFC receives a call for heat.
The furnace IFC will repeat the inducer motor learning
routine after:
150 Cycles in First Stage Heat
100 Cycles in Second Stage Heat
50 Cycles in third Stage Heat
The furnace IFC checks the pressure switches PS-1 and
PS-2 after a call for heat from the comfort control. They
both have to be open before a heating cycle can begin.
The furnace IFC sends a digital signal to the variable speed
inducer drive to run the inducer motor at the preset
factory second stage heat RPM.
The furnace IFC waits for the PS-1 and PS-2 pressure
switches to close. A 24 Volt AC signal is sent to the furnace IFC
when a pressure switch closes.
The furnace IFC will continue to signal the variable speed
inducer drive to increase the inducer speed in steps if
PS-1 and PS-2 are not closed when the preset factory
second stage heat RPM is reached. The maximum RPM for
stage two is set at 4400 RPM.
When PS-1 and PS-2 switches close, the furnace IFC
will then start the ignition cycle.
The IFC now starts the igniter warm up cycle.
Near the end of the warm up cycle the furnace IFC will turn
on the gas valve.
When the burner flame is detected by the furnace IFC, a 45
second time delay for indoor blower operation begins. The
forty-five second time delay allows the heat exchanger and the
recuperative cell to warm up. By the end of this delay time, the
inducer discharge air temperature will be at its operating
temperature and the density of the products of combustion will
be stabilized.
The furnace IFC now signals the variable speed indoor
blower to run at the programmed second stage heating
airflow.
The furnace IFC will now start its inducer second stage
heat airflow learning routine.
The furnace IFC will signal the variable speed inducer drive
beginning to reduce the inducer motor speed in steps
until the furnace IFC detects that PS-2 is open.
When PS-2 opens the furnace IFC will NOTE the inducer
motor RPM.
The furnace IFC then adds an additional number of RPM to
the inducer motor second stage NOTED RPM until PS-2 closes.
The additional number of RPM plus this NOTED RPM is the learned
second stage inducer operating RPM.
The furnace IFC now stores this learned operating inducer
RPM for second stage heat in its memory.
The furnace IFC will use this stored learned operating inducer
RPM for second stage heat calls it receives in the future.
If the furnace IFC is still receiving only a call for first stage
operation it will now start the learning routine for first stage.
The furnace IFC will then continue to reduce the inducer motor
RPM in steps until the furnace IFC detects that PS-1 is open.
When PS-1 opens, the furnace IFC signals the motor drive
to increase the inducer speed by an additional number of
RPM. This is the learned operating speed. The furnace IFC will
note this inducer motor RPM.
The furnace IFC then adds an additional number of RPM to
the first stage NOTED RPM until PS-1 closes.
The furnace IFC now stores this learned operating inducer
RPM in its memory and uses it for first stage heat calls it receives
in the future.
The IFC signals the indoor variable speed blower to operate
at the programmed first stage heating airflow.
Whenever the furnace is powered up or after a RESET, the
furnace IFC will not go through a learning routine for the third
stage of heat until it receives a call for the third stage of heat.
Third stage inducer learning routine
When the furnace IFC receives a digital signal for the third
stage of heat from the comfort control it will begin the inducer
motor learning routine for third stage heat.
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UH3 Inducer Learning Routine Sequence
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