American Standard UHMB060ACV3VB Series Service Facts page 16

Service Facts
IFC INDUCER LEARNING ROUTINE SEQUENCE
Note:
Stage 1 = 40% (low) heat, Stage 2 = 100% (high) heat
•
The furnace IFC will go through an inducer learning
routine for three pressure switches.
•
The learning routine is done to determine the
correct amount of ventilation air for complete
combustion.
• The inducer motor speed may be different for each
installation due to the different length and size of the
ventilation pipe, exhaust vent pipe, number of pipe
fittings used, and the type of vent cap installed.
•
The inducer learning routine is repeated each time
the power to the furnace is interrupted. Once power
is restored and the furnace receives a call for heat,
the PS-1, PS-2 inducer learning routine will be initi-
ated. The furnace IFC will not go through a PS-3 in-
ducer learning routine until it receives a call for 100%
(high) heat.
• To ensure the furnace heating efficiency is maintained
the furnace IFC will repeat the inducer motor learning
routine after :
150 Cycles at 40% (low) heat
100 Cycles at 65% (medium) heat
50 Cycles at 100% (high) heat
PS-1, PS-2 Inducer Learning Routine
•
The furnace IFC checks the pressure switches PS-
1, PS-2 and PS-3. They all 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 65% (medium) 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.
•
If PS-1 and PS-2 do not close at the preset factory
65% (medium) heat RPM, the furnace IFC will con-
tinue to signal the variable speed inducer drive to
increase the inducer speed in steps until PS-1 and
PS-2 close or until the maximum RPM for 65% (me-
dium) heat is reached.
•
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.
NOTE: The furnace lights at approximately 65% of
capacity.
•
When the burner flame is detected by the furnace
IFC, a forty-five second time delay for indoor blower
16
operation begins. The forty-five second time delay
allows the heat exchanger and the recuperative
cell to warm up.
•
The furnace IFC will now start its 65% (medium)
heat inducer learning routine.
•
The furnace IFC will signal the variable speed in-
ducer 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 65% (medium) heat inducer motor
NOTED RPM until PS-2 closes.
•
The additional number of RPM plus this NOTED
RPM is the learned 65% (medium) heat inducer
operating RPM.
•
The furnace IFC now stores this learned operating
inducer RPM for 65% (medium) heat in its memory.
•
The furnace IFC will use this stored learned
operating inducer RPM for 65% (medium) heat
calls it receives in the future.
•
If the furnace IFC is still receiving a call for
low heat operation it will now start the learning rou-
tine for 40% (low) heat.
•
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 will NOTE the
inducer motor RPM.
• The furnace IFC then adds an additional number of
RPM to the 40% (low) heat inducer motor NOTED
RPM until PS-1 closes.
•
The additional number of RPM plus this NOTED
RPM is the learned 40% (low) heat inducer operat-
ing RPM.
•
The furnace IFC now stores this learned inducer
operating RPM for 40% (low) heat in its memory.
• The furnace IFC will use this stored learned inducer
operating RPM for 40% (low) heat calls it receives
in the future.
•
Whenever the furnace is powered up or after a RE-
SET, the furnace IFC will not go through a learning
routine for 100% (high) heat until it receives a call
for 100% (high) heat.
UHM-DHM-SF-1V-EN