Installation Guide

42
SYSTEM TROUBLESHOOTING
NOTE: Refer to the instructions accompanying the ComfortNet
compatible outdoor AC/HP unit for troubleshooting information.
Refer to the Troubleshooting Chart in the back of this manual
for a listing of possible furnace error codes, possible causes
and corrective actions.
N ORMAL S EQUENCE OF O PERATION
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 displays 8 8 on dual 7-
segment display LED’s.
• Integrated control module monitors safety circuits
continuously.
• Furnace awaits call from thermostat. Dual 7-segment
LED’s display O 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,
delivering 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 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 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
fifteen 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 duration 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,
initiating 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
selected ramping profile. Electronic air cleaner
terminal is energized with circulator blower.
• Furnace circulator blower and outdoor cooling unit
run their appropriate speeds, integrated control
module monitors safety circuits continuously.
• R and Y1/G or Y2/G thermostat contacts open,
completing 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.