GC9C96 Service Manual
SYSTEM OPERATION
13
• Fixed time options are expressed in minutes on the
display as: 10203060
• If AUt (Automatic) is selected, the actual timing for the
transition to 2nd stage heat will be calculated by the
control board based on length of run time of previous
heating cycles (duty cycle).
• Press the center switch to save the selection.
In Auto mode, the transition to 2nd stage heat will vary
between 1 to 12 minutes.
Duty Cycle %
Heating Stage Timing
Demand
0-38
1
st
Stage, 12 minute 2
nd
Stage
Light
39-50
1
st
Stage, 10 minute 2
nd
Stage
Light to Average
51-62
1
st
Stage, 7 minute 2
nd
Stage
Average
63-75
1
st
Stage, 5 minute 2
nd
Stage
Average to Heavy
76-88
1
st
Stage, 3 minute 2
nd
Stage
Heavy
89-100
1
st
Stage, 1 minute 2
nd
Stage
Heavy
• The furnace is setup by default to use a two-stage
heating thermostat.
• The menu may be accessed by pressing the Left or Right
menu switches to get to theAHSmenu.
• The menu will display these options: no10203060
AUt
• Select no.
• Press the center switch to save the selection.
• In this mode only a W2 signal on the control board will
bring on 2nd stage heat.
This furnace can be used in conjunction with a heat pump
in a fossil fuel application. A fossil fuel application refers to
a combined gas furnace and heat pump installation which
uses an outdoor temperature sensor to determine the most
cost ecient means of heating (heat pump or gas furnace).
A heat pump thermostat with three stages of heat is required
to properly use a two-stage furnace in conjunction with a heat
pump. Refer to the fossil fuel kit installation instructions for
additional thermostat requirements.
Strictly follow the wiring guidelines in the fossil fuel kit
installation instructions. All furnace connections must be made
to the furnace two-stage integrated control module and the
“FURNACE” terminal strip on the fossil fuel control board.
Two furnaces of the same model may be twinned. The
integrated control board has a 3/16” terminal labeled “TWIN”
located beside the low voltage thermostat connection strip.
Twinning allows simultaneous operation of two furnaces and
forces the indoor blower motors of each furnace to operate
synchronously into a common duct system. Using the twinning
function will require only eld installed wiring with no external
kits or parts. The staging and speed tap options must be set
the same on both furnaces.
Each furnace must be connected to it’s own 115 VAC
power supply. The L1 connection to each furnace must be in
phase (connected to circuit breakers on the same 115 VAC
service panel phase leg). To verify that the furnaces are in
phase, check from L1 to L1 on each furnace with a voltmeter. If
the furnaces are in phase, the voltage between both furnaces
will be ZERO.
ROOM THERMOSTAT
Y2
Y/Y1
C
G
R
W/W1
W2
Y2
Y/Y1
C
G
R
W/W1
W2
Y2
Y/Y1
C
G
R
W/W1
W2
TWIN
TWIN
COND UNIT
CONTACTOR
COND UNIT
CONTACTOR
FURNACE 1
FURNACE 2
The furnace integrated control module is equipped with
line voltage accessory terminals for controlling power to an
optional eld-supplied humidier and/or electronic air cleaner.
The accessory load specications are noted in the chart
below:
Humidifier
1.0 Amp maximum at 120 VAC
Electronic Air Cleaner
1.0 Amp maximum at 120 VAC
Turn OFF power to the furnace before installing any
accessories. Follow the humidier or air cleaner manufac-
turers’ instructions for locating, mounting, grounding, and
cotrolling these accessories. Accessory wiring connections
are to be made through the 1/4” quick connect terminals
provided on the furnace integrated control module. The
humidier and electronic air cleaner hot terminals are iden-
tied as HUM H and EAC H. The humidier and electronic
air cleaner neutral terminals are identied as NEUTRAL. All
eld wiring must conform to applicable codes. Connections
should be made as shown.
If it is necessary for the installer to supply additional line
voltage wiring to the inside of the furnace, the wiring must
conform to all local codes, and have a minimum temperature
rating of 105°C. All line voltage wire splices must be made