Goodman ACVC96 BA Series Service And Troubleshooting page 36

SYSTEM OPERATION
The following stipulations apply when connecting gas piping.
Diagnostics
Accessing the furnace's diagnostic menu provides access to
the last six faults detected by the furnace. Faults are stored
most recent to least recent, Any consecutively repeated fault is
stored a maximum of three times. Example: A clogged return
air filter causes the furnace limit to trip repeatedly. The control
will only store this fault the first three consecutive times the
fault occurs. Navigate to the diagnostics menu as described
above in the thermostat installation manual.
NOTE: It is highly recommended that the fault history be
cleared when performing maintenance or servicing the
furnace.
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 monitors safety circuits
continuously.
• Furnace awaits call from thermostat. 7-segment LED's
display   while awaiting call from thermostat.
Heating Mode
The normal operational sequence in heating mode is
as follows:
• W thermostat contact closes, 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.
• Induced draft blower steps to low speed following
prepurge. Low stage pressure switch contacts are
closed.
• Igniter warm up begins upon Inducer draft blower 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.
• Based on the furnace internal control algorithms the gas
valve and induced draft blower may continue operating
on low stage or both will change to high stage. After
a power cycle, the first heat call will result in high
stage operation.
• Circulator blower is energized on heat speed following
the selected blower on delay and will begin to ramp
up. Electronic air cleaner terminal is energized with
circulator blower.
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• Furnace is now operating on the specified stage
determined by the internal control algorithm.
• Furnace runs, integrated control module monitors
safety circuits continuously.
• If the internal algorithm 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 internal algorithm 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.
• W thermostat contacts open, completing the call for heat.
• Gas valve closes, extinguishing flame.
• Induced draft blower is de-energized following a 15
second post purge.
• Circulator blower continues running for the selected
heat off delay period. 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. 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 remainder
of the heat off delay period.
• Circulator blower and electronic air cleaner terminal are
de-energized.
• Circulator blower shuts off after the heat off delay period
expires.
• Furnace awaits next call from thermostat.
Operational Checks
The burner flames should be inspected with the burner
compartment door installed. Flames should be stable, quiet,
soft, and blue (dust may cause orange tips but they must not be
yellow). Flames should extend directly outward from the burners
without curling, floating, or lifting off. Flames must not impinge on
the sides of the heat exchanger firing tubes.
Safety Circuit Description
A number of safety circuits are employed to ensure safe and
proper furnace operation. These circuits serve to control any
potential safety hazards and serve as inputs in the monitoring and
diagnosis of abnormal function. These circuits are continuously
monitored during furnace operation by the integrated control
module.
Integrated Control Module
The integrated control module is an electronic device which, if
a potential safety concern is detected, will take the necessary
precautions and provide diagnostic information through an LED.