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Heating Sequence of Operation
The integrated control initiates a pressure switch
calibration at the initial unit start-up on a call for heat. The
ignition control will also initiate a calibration any time main
power is turned off and back on and a heating demand
is present. Additional calibrations may be initiated by the
service technician during field test sequence. The following
heating sequence of operation assumes completion of a
successful calibration.
NOTE: In Comfort Sync communicating applications,
the sequence of operation is the same but all DIP switch
settings are overridden by the thermostat.
NOTE: The thermostat selection DIP switch on the
integrated control is factory set in the "TWO STAGE"
position.
Applications Using a Two Stage Thermostat
A-Heating Sequence - Control Thermostat Selection
DIP Switch in "Two Stage" Position (Factory Settling)
1.
On a call for heat, thermostat first stage contacts
close, sending a signal to the integrated control. The
integrated control runs a self diagnostic program and
checks high temperature limit switches for normally
closed contacts and pressure switches for normally
open contacts. The combustion air inducer is energized
at ignition speed, which is approximately the same as
the inducer speed at 70 percent firing rate.
2.
Once the control receives a signal that the low fire
pressure switch has closed, the combustion air inducer
begins a 15 second pre-purge in the ignition speed.
3.
After the pre-purge is complete, a 20 second initial
ignitor warm up period begins. The combustion air
inducer continues to operate at the ignition speed.
4.
After the 20 second warm up period has ended, the
gas valve is energized and ignition occurs. At the
same time, the control module sends a signal to
begin an indoor blower 30 second ON delay. When
the delay ends, the indoor blower motor is energized
at a speed that matches the firing rate. After the 10
second ignition stabilization delay expires, the inducer
speed is adjusted to the appropriate target rate. The
inducer will remain at the 70 percent speed as long as
the thermostat has a first stage heating demand.
5.
If second stage heat is required, the thermostat
second stage heat contacts close and send a signal to
the integrated control. The integrated control initiates
a 30 second second stage recognition delay.
6.
At the end of the recognition delay and on all
subsequent calls for heat in the same heating cycle,
the integrated control energizes the combustion air
inducer at high speed. The control also checks the
high fire pressure switch to make sure it is closed.
As the inducer speed is increased to high, the indoor
blower motor is adjusted to a speed appropriate for the
508364-01
target rate.
7.
When the demand for high fire (second stage) heat
is satisfied, the gas valve is de-energized and the
field selected indoor blower off delay begins. The
combustion air inducer begins a 20 second post purge
period.
8.
When the combustion air post purge period is
complete, the inducer is de-energized. The indoor
blower is deenergized at the end of the off delay.
B - Heating Sequence - Control Thermostat Selection
DIP Switch in "Variable Capacity" Position
1.
On a call for heat, thermostat first stage contacts
close, sending a signal to the integrated control. The
integrated control runs a self diagnostic program and
checks high temperature limit switches for normally
closed contacts and pressure switches for normally
open contacts. The combustion air inducer is energized
at ignition speed, which is approximately the same as
the inducer speed at 70 percent firing rate.
2.
Once the control receives a signal that the low fire
pressure switch has closed, the combustion air inducer
begins a 15 second pre-purge in low speed.
3.
After the pre-purge is complete, a 20 second initial
ignitor warm up period begins. The combustion air
inducer continues to operate at the ignition speed.
4.
After the 20 second warm up period has ended, the
gas valve is energized and ignition occurs. At the same
time, the control module begins an indoor blower 30
second ON delay. When the delay ends, the indoor
blower motor is energized at a speed that matches
the firing rate. After the 10 second ignition stabilization
delay expires, the inducer speed is adjusted to the
appropriate target rate. If the furnace is operating in
the initial heating cycle after power up, the initial firing
rate will be approximately 35 percent. The firing rate
on subsequent cycles will be automatically adjusted
by the integrated control based on thermostat cycles.
The firing rate will vary and will range from 35 percent
to 90 percent. The furnace will continue this operation
as long as the thermostat has a first stage heating
demand.
5.
If second stage heat is required, the thermostat
second stage heat contacts close and send a signal
to the integrated control. The integrated control either
increases the firing rate to 70 percent (if the current
rate is at or below 60 percent) or increases the
firing rate by 10 percent (if the current rate is above
60 percent). If the call for heat continues 5 minutes
beyond this initial upstage, the rate will be increased
by 10 percent every 5 minutes until the call for heat
is satisfied or the furnace reaches 100 percent rate.
As the firing rate increases, the indoor blower motor
is adjusted to a speed appropriate for the target rate.
6.
If second-stage heat demand is satisfied, but first stage
is still present, the furnace will continue to operate at
Issue 2346
Page 55 of 74
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