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Power Up
The normal power up sequence is as follows:
115 VAC power applied to furnace.
Integrated control module performs internal checks.
Integrated control module LED will light.
Integrated control module monitors safety circuits
continuously.
Furnace awaits call from thermostat.
Heating Mode—Mode DIP Switch Set to
1 STG Position
The normal operational sequence in heating mode is as follows:
R and W thermostat contacts close, initiating a call for heat.
Integrated control module performs safety circuit checks.
Induced draft blower is energized for a 15-second prepurge
period causing the pressure switch contacts to close.
Igniter warm up begins after 15-second prepurge expires.
Low-stage and high-stage gas control valves open at the end
of the igniter warm up period, delivering gas to the burners
and establishing flame.
Integrated control module monitors flame presence. Gas
control valve will remain open only if flame is detected.
Circulator blower is energized on high heat speed following a
fixed 30-second blower on delay. Electronic air cleaner
terminals are energized with circulator blower.
Furnace operates; integrated control module monitors safety
circuits continuously.
R and W thermostat contacts open, completing the call for
heat.
Gas control valve closes, extinguishing flame.
Induced draft blower is de-energized following a 15-second
post purge.
The circulator blower remains at high heat speed for
30 seconds. The circulator blower then switches to low heat
speed for the remainder of the selected heat off delay period.
For example, the selected heat off delay period is
150 seconds. The circulator blower operates at high heat for
30 seconds and at low speed for 150 - 30 = 120 seconds.
Circulator blower and electronic air cleaner terminals are de-
energized.
Circulator blower ramps down to OFF during the 30 seconds
following the heat off delay period.
Furnace awaits next call from thermostat.
Heating Mode—Mode DIP Switch Set to
2 STG Position
The normal operational sequence in heating mode is as follows:
R and W thermostat contacts close, initiating a call for heat.
Integrated control module performs safety circuit checks.
Induced draft blower is energized for a 15-second prepurge
period causing the pressure switch contacts to close.
Igniter warm up begins after 15-second prepurge expires.
SEQUENCE OF OPERATION
Low-stage and high-stage gas control valves open at the end
of the igniter warm up period, delivering gas to the burners
and establishing flame.
High-stage gas control valve closes after 5 seconds;
low-stage gas control valve remains open.
Integrated control module monitors flame presence. Gas
control valve will remain open only if flame is detected.
Circulator blower is energized on low-heat speed following a
fixed 30-second blower on delay. Electronic air cleaner
terminals are energized with circulator blower.
Furnace is now operating in low-stage heating mode.
Furnace operates; integrated control module monitors safety
circuits continuously.
If low-stage delay period expires, control will shift operation
from low-stage heating mode operation to high-stage heating
mode operation. Control will energize circulator blower
high-heat speed and high-stage gas control valve.
Furnace is now operating in high-stage heating mode.
R and W thermostat contacts open, completing the call for
heat.
Induced draft blower is de-energized following a 15-second
post purge.
Circulator blower is de-energized following a heat off delay
period (selectable 100 to 150 seconds; factory-set at
150 seconds).
If the furnace is operating in the low-stage heating mode
when thermostat contacts open, circulator remains at
low-heat speed for the selected delay off period. If the
furnace is operating in high-stage heating mode when the
thermostat contacts open, the circulator blower remains at
high-heat speed for 30 seconds. The circulator blower then
switches to low-heat speed for the remainder of the
selected heat off delay period. For example, the selected
heat off delay period is 150 seconds. The circulator blower
operates at high heat for 30 seconds and at low speed for
150 - 30 = 120 seconds.
Furnace awaits the next call from thermostat.
Cooling Mode
The normal operational sequence in cooling mode is as follows:
R and Y thermostat contacts close, initiating a call for cool.
Integrated control module performs safety circuit checks.
Outdoor fan and compressor are energized.
Circulator blower is energized on cool speed following a fixed
5-second on delay. Electronic air cleaner terminals are
energized with circulator blower.
Furnace circulator blower and outdoor cooling unit run;
integrated control module monitors safety circuits
continuously.
R and Y thermostat contacts open, completing the call for
cool.
Outdoor fan and compressor are de-energized.
Circulator blower is de-energized following a fixed 45-second
cool off delay period. Electronic air cleaner terminals are
de-energized.
Furnace awaits the next call from thermostat.
35
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