SYSTEM OPERATION
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NORMAL SEQUENCE OF OPERATION
POWER UP
The normal power up sequence is as follows:
• 115 VAC power applied to furnace. Integrated con-
trol module performs internal checks.
• Integrated control module displays 8
8 on dual 7-seg-
ment display LED’s.
• Integrated control module monitors safety circuits con-
tinuously.
• Furnace awaits call from thermostat. Dual 7-segment
LED’s display 0
N while awaiting call from thermostat.
HEATING MODE
The normal operational sequence in heating mode is as
follows:
• R and W1 (or R and W1/W2) thermostat contacts
close, initiating a call for heat.
• Integrated control module performs safety circuit
checks.
• Induced draft blower is energized on high speed for a
15-second prepurge. Humidifier terminal is energized
with induced draft blower.
• Induced draft blower steps to low speed following
prepurge. Low stage pressure switch contacts are
closed.
• Igniter warm up begins upon step to low speed and
presence of closed low stage pressure switch contacts.
• Gas valve opens at end of igniter warm up period, de-
livering gas to burners and establishing flame.
• Integrated control module monitors flame presence.
Gas valve will remain open only if flame is detected.
• If the thermostat call is for low heat, gas valve and
induced draft blower will continue on low stage. If the
call is for high heat, the gas valve and induced draft
blower will change to high stage.
• Circulator blower is energized on heat speed following
a thirty (30) second blower on delay. The circulator
blower requires thirty seconds to ramp up to full speed.
Electronic air cleaner terminal is energized with circu-
lator blower.
• Furnace is now operating on the specified stage called
for by the two-stage thermostat.
• Furnace runs, integrated control module monitors
safety circuits continuously. If the two-stage thermo-
stat changes the call from low heat to high heat, the
integrated control module will immediately switch the
induced draft blower, gas valve, and circulator blower
to their high stage settings.
• If the two-stage thermostat changes the call from high
heat to low heat, the control will immediately switch
the induced draft blower and gas valve to their low
stage settings. The circulator blower will remain on
high heating speed for thirty (30) seconds before
switching to the low heat circulating speed.
• R and W1 (or R and W1/W2) thermostat contacts
open, completing the call for heat.
• Gas valve closes, extinguishing flame.
• Induced draft blower is de-energized following a fif-
teen second post purge. Humidifier terminals are de-
energized.
• Circulator blower continues running for the selected
heat off delay period (90, 120, 150 or 180 seconds).
The speed run during this period depends on the last
heat call provided by the thermostat.
If the last call for heat was a call for low heat, the air
circulator motor will run on low heat speed for the du-
ration of the heat off delay period (90, 120, 150 or 180
seconds).
If the last call for heat was a call for high heat, the air
circulating motor will run on the high heating speed for
thirty (30) seconds and then switch to the low heating
speed for the balance of the heat off delay period (60,
90, 120 or 150 seconds).
• Circulator blower and electronic air cleaner terminal
is de-energized.
• Circulator blower ramps down to OFF during the 30
seconds following the heat off delay period.
• Furnace awaits next call from thermostat.
COOLING MODE
The normal operational sequence in cooling mode is as
follows:
• R and Y1/G or Y2/G thermostat contacts close, initi-
ating a call for cool.
• Integrated control module performs safety circuit
checks.
• Outdoor fan and compressor are energized to their
appropriate speed.
• Circulator blower is energized on the appropriate cool
speed at the level and time determined by the se-
lected ramping profile. Electronic air cleaner terminal
is energized with circulator blower.
• Furnace circulator blower and outdoor cooling unit
run their appropriate speeds, integrated control mod-
ule monitors safety circuits continuously.
• R and Y1/G or Y2/G thermostat contacts open, com-
pleting the call for cool.
• Outdoor fan and compressor are de-energized.
• Circulator blower continues running during a cool off
delay period. The OFF delay time and airflow level are
determined by the selected ramping profile.
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