GC9C80 Service Manual
SERVICING
29
The following drawing illustrates the style of limit switches
used on the 90% furnaces.
ENCLOSED DISK
FRONT VIEW SIDE VIEW
G
TG
T
R BR RG R
GG TR RG
T R
R B RT
R T
RRT G R JR R T
1. Remove burner compartment door to gain access to
the primary limit.
2. Remove low voltage wires at limit control terminals.
3. With an ohmmeter, test between these two terminals
as shown in the following drawing. The ohmmeter
should read continuous unless heat exchanger tem-
perature is above limit control setting. If not as above,
replace the control.
If the control detects the high limit circuit open, the RED LED
will ash FOUR times and energize the inducer and indoor
blower.
If the limit circuit opens ve times within a single call for heat,
the furnace will go into lockout for one hour. The RED LED
will display a FOUR ash code during this time. The control
board can be reset by cycling 115 volt power to the furnace.
If the limit circuit opens and does not close within ve minutes,
the control assumes the blower has failed the RED LED will
ash ELEVEN times.
If the limit circuit opens and does not close within fteen
minutes, the control assumes the manual rollout or fuse
has opened and the RED LED will ash FIVE times. The
control will enter a one hour lockout and the inducer will run
continuously.
In an open limit condition the red LED will ash as described
above but the error code will not be stored in memory until
the limit resets or until 15 minutes has elapsed. So if the limit
resets in less than 5 minutes a four ash code will be stored.
If the limit resets in more than 5 but less than 15 minutes, an
eleven ash code will be stored. If the limit is still open after
15 minutes, a ve ash code will be stored.
COLOR
IDENTIFYING
TAB
4. After completing check and/or replacement of primary
limit control, reinstall burner compartment door.
5. Turn on electrical power and verify proper unit operation.
The auxiliary limit control is designed to prevent furnace
operation in case of main blower failure in horizontal
installations. It may also open if the power supply is interrupted
while the furnace is ring.
The auxiliary limit control is suitable for both horizontal
right and horizontal left installations. Regardless of airow
direction, it does not need to be relocated. The (2) two auxiliary
limits are located on the blower housing (one on each side),
as shown in the following illustration.
LIMIT
AUXILIARY LIMIT
CONTROL
AUXILIARY LIMIT
CONTROL
BLOWER HOUSING