GC9C80 Service Manual
SERVICING
34
2. Turn on gas to furnace and check for leaks. If leaks are
found, repair and then reinstall burner compartment door.
3. Turn on electrical power and verify proper unit operation.
Make sure furnace operates at the proper manifold
pressure at both high and low stage outputs.
High Stage 3.2 to 3.8" w.c. 3.5" w.c.
Low Stage 1.6 to 2.2" w.c. 1.9" w.c.
G
TG
T
TR R T G
BR RG R TG
High Stage
9.7 to 10.3" w.c.
10.0" w.c.
Low Stage
5.7 to 6.3" w.c.
6.0" w.c.
use a 120V silicon
nitride ignitor for ignition. The normal operating temperature
is approximately 2156°F - 2678°F. At room temperature the
igniter ohm reading should be from 37-68 ohms.
7. Place unit in heating cycle, measure current draw of ignitor
during preheat cycle.
The steady state current at 120V is 0.37 to 0.68 amps.
8. After checking and/or replacing of hot surface ignitor,
reinstall burner compartment door and verify proper unit
operation.
Flashback will also cause burning in the burner venturi, but is
caused by the burning speed being greater than the gas-air
ow velocity coming from a burner port.
Flashback may occur at the moment of ignition, after a burner
heats up or when the burner turns o. The latter is known as
extinction pop.
Since the end results of ashback and delayed ignition can
be the same (burning in the burner venturi) a denite attempt
should be made to determine which has occurred.
If ashback should occur, check for the following:
1. Improper gas pressure - adjust to proper pressure.
2. Check burner for proper alignment and/or replace burner.
3. Improper orice size - check orice for obstruction.
The pressure control is a safety device to prevent the
combustion cycle from occurring with inadequate venting
caused by a restricted or blocked vent pipe.
1. Remove burner compartment door to gain access to
pressure switch(es).
2. Remove wires from the pressure switch(es) electrical
terminals.
3. Remove the pressure control hose from the control and
interconnect with an manometer as shown in the following
gures.
4. With an ohm meter connected across the pressure switch
terminals; with the inducer running the switch should close
and the ohm meter should show a complete circuit across
the pressure switch. If the switch is not closed, compare
the negative pressure to the closing point specied for
the particular switch. Either the switch is defective or the
inducer / venting system is inadequate.
-.
OPEN TO
ATMOSPHERE
HOSE TO INDUCED
DRAFT BLOWER TAP
1/4" TEE
INDUCED DRAFT BLOWER
PRESSURE SWITCH
PRESSURE SWITCH
HOSE
INDUCED
DRAFT
BLOWER
*
*
*
* *
*
*
M
1
2
3P
C
ON
O
F
F
COIL COVER
PRESSURE SWITCH
The furnace as shipped requires no change to run between
0 - 7500 feet. Do not attempt to increase the ring rate
by changing orices or increasing the manifold pressure
below 7500 feet. feet. This can cause poor combustion and
equipment failure. High altitude installations above 7500
feet. feet may require both a pressure switch and an orice
change. These changes are necessary to compensate for
the natural reduction in the density of both the gasfuel and
the combustion air at higher altitude.