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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 control module performs internal checks.
• Integrated control module flashes LED one time.
• Integrated control module monitors safety circuits continuously.
• Furnace awaits call from thermostat.
The normal operational sequence in heating mode is as follows:
Heating Mode
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 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 fifteen
second post purge. Humidifier terminals are de-ener-
gized.
•
Circulator blower continues running for the selected
heat off delay period (60, 90, 120, 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
duration of the heat off delay period (60, 90, 120, 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 seconds and then switch to the low heating
speed for the
balance
of the heat off delay period (30,
60, 90, or 150 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.
•
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
10-second prepurge. Humidifier terminals are ener-
gized 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 con-
tacts.
•
Gas valve opens at end of igniter warm up period,
delivering gas to burners and establishing flame.
•
Integrated control module monitors flame presence.
Gas valve will remain open only if flame is sensed.
• 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 the appropriate heat
speed following a fixed thirty second blower on delay.
The circulator blower requires 30 seconds to ramp up
to full speed. Electronic air cleaner terminals are
energized with circulator 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 thermostat changes the call from low
