GC9C80 Service Manual
SYSTEM OPERATION
9
W2 W/W1 R G C Y/Y1 Y2
24V HUM
Terminal is
energized when
pressure switch
is closed
24 VOLT HUM.
& HUMIDISTAT
• On a call for heat, the thermostat contacts close & the
control board receives 24 VAC on the W1 terminal.
• The control board microcomputer runs its self-check
routine.
• The control veries the limit switch is closed (24 VAC on
Pin 8 of the 12 Pin connector).
• The control veries that pressure switch circuit is open
(0 VAC on Pin 5).
• The control module performs a gas valve circuitry check
to verify gas valve relay state and presence of voltage
at the valve.
• The system will energize the Induced draft blower.
• The pre-purge period begins once the low re pressure
switch is detected closed (24 VAC on Pin 5).
• After the completion of pre-purge, the control will
energize the igniter.
• After completion of the ignitor warm-up period:
• The gas valve is energized.
• The ignitor is de-energized as soon as ame is sensed.
• After 30 seconds the indoor blower is energized on
heating speed.
• When using a single-stage heating thermostat, the
furnace will transition to 2nd stage gas heat by either a
xed time or auto mode depending on menu selections
made by the installer.
• The inducer motor is enabled at high speed.
• Closure of the 2nd stage pressure switch will energize
the high re stage of the gas valve.
• The 2nd stage gas heat speed of the indoor blower is
energized
• When the thermostat is satised:
• The gas valve is de-energized.
• The inducer remains energized for the post purge period
(15 seconds).
• The indoor blower runs for the selected o delay period
(90 seconds by default, adjustable from 30 – 180
seconds).
• The control board receives a 24 VAC signal on the W2
terminal.
• The inducer motor is enabled at high speed.
• Closure of the 2nd stage pressure switch will energize
the high re stage of the gas valve.
• The 2nd stage gas heat speed of the indoor blower is
energized.
To change the main blower speed in HEATING mode, follow
the following steps:
Press the left or right switch until LED displays “gA1”
(for single-stage HEATING) or “gA2” (for two-stage
HEATING). Press the center switch and LED will display
the selected speed number as Fxx (xx: Blower speed
number).
The control will rotate available speed number every time
left / right switches are pressed. The table below shows
the available speeds for low & high heat mode.
Press the center switch to save the selection.
Always refer to the Heating Chart to choose from
available heating speeds
THERMOSTATCALL AVAILABLESPEEDS
W/W1
F01(DEFAULT)
F03
F04
W2
F02(DEFAULT)
F04
F05
To change the main blower speed in circulation mode, follow
the following steps:
Press the left or right switch until LED displays “FSd”. Press
the center switch and LED will display the selected speed
number as Fxx (xx: Blower speed number from 1 to 9).
F03 is the default speed for circulation.