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Applications Using a Two-Stage Thermostat
A - Heating Sequence -- Integrated Control Thermo-
stat Selection DIP Switch 1 OFF in “Two-Stage” Posi-
tion (Factory Setting)
1 - On a call for heat, thermostat rst-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 low speed.
2 - Once the control receives a signal that the low
pressure switch has closed, the combustion air
inducer begins a 15-second pre-purge in low speed.
NOTE - If the low re pressure switch does not close
the combustion air inducer will switch to high re.
After a 15 second pre-purge the high re pressure
switch will close and the unit will begin operation on
high re. After 10 to 20 seconds of high re operation
the unit will switch to low re.
3 - After the pre-purge is complete, a 20-second initial
ignitor warm-up period begins. The combustion air
inducer continues to operate at low speed.
4 - After the 20-second warm-up period has ended,
the gas valve is energized on low re (rst stage)
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 on the low re
heating speed, the HUM contacts close energizing
the humidier and 120V ACC terminal is energized.
The furnace will continue this operation as long as
the thermostat has a rst-stage heating demand.
NOTE - If the indoor thermostat is set on
CONTINUOUS FAN ON mode, the furnace will
light on high re (second-stage) for 60 seconds to
improve heat exchanger warm up. After 60 second
warm-up period, furnace will switch to low re (rst-
stage).
5 - I f 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, the integrated
control energizes the combustion air inducer at
high speed. The control also checks the high re
(second stage) pressure switch to make sure it is
closed. The high re (second stage) gas valve is
energized and the indoor blower motor is energized
for operation at the high re heating speed.
7 - When the demand for high re (second stage) heat
is satised, the combustion air inducer is switched
to the low-re heating speed and the high-re
(second stage) gas valve is de-energized. The
low-re (rst stage) gas valve continues operation.
The indoor blower motor is switched to the low-re
heating speed.
8 - When the thermostat demand for low-re (rst
stage) heat is satised, the gas valve is de-
energized and the eld-selected indoor blower o
delay begins. The combustion air inducer begins a
5-second post-purge period.
9 - When the combustion air post-purge period is
complete, the inducer, the HUM contacts as well
as the 120V ACC terminals are de-energized. The
indoor blower is de-energized at the end of the o
delay.
Applications Using A Single-Stage Thermostat
B - Heating Sequence -- Integrated Control Thermostat
Selection DIP Switch 1 ON in “Single-Stage” Position
NOTE - In these applications, two-stage heat will be initi-
ated by the integrated control if heating demand has not
been satised after the eld adjustable period (7 or 12
minutes).
1 - On a call for heat, thermostat rst-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 low speed.
2 - Once the control receives a signal that the low
pressure switch has closed, the combustion air
inducer begins a 15-second pre-purge in low speed.
NOTE - If the low re pressure switch does not close
the combustion air inducer will switch to high re.
After a 15 second pre-purge the high re pressure
switch will close and the unit will begin operation on
high re After 10 to 20 seconds of high re operation
the unit will switch to low re.
3 - After the pre-purge is complete, a 20-second initial
ignitor warm-up period begins. The combustion air
inducer continues to operate at low speed.
4 - After the 20-second warm-up period has ended,
the gas valve is energized on low re (rst stage)
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 on the low re
heating speed and the HUM contacts are energized.
The integrated control also initiates a second-stage
on delay (factory-set at 7 minutes; adjustable to 12
minutes).
5 - If the heating demand continues beyond the
second-stage on delay, the integrated control
energizes the combustion air inducer at high speed.
The control also checks the high re (second stage)
pressure switch to make sure it is closed. The high
re (second stage) gas valve is energized and the
indoor blower motor is energized for operation at
the high re heating speed.
6 - When the thermostat heating demand is satised,
the combustion air inducer begins a 5-second low
speed post-purge. The eld-selected indoor blower
o delay begins. The indoor blower operates at the
low-re heating speed.
7 - When the combustion air post-purge period is
complete, the inducer, the HUM contacts as well
as the 120V ACC terminals are de-energized. The
indoor blower is de-energized at the end of the o
delay.
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