SERVICE AND TECHNICAL SUPPORT MANUAL
Gas Furnace: (F/G)9MXT
Specifications subject to change without notice.
440 04 4321 02
13
Figure 7
Typical TwoStage Field Wiring Diagram
115-VOLT FIELD-
SUPPLIED
FUSED
DISCONNECT
JUNCTION
BOX
CONTROL
BOX
24-VOLT
TERMINAL
BLOCK
THREE-WIRE
HEATING-
ONLY
FIVE
WIRE
NOTE 2
NOTE 1
1-STAGE
THERMOSTAT
TERMINALS
FIELD-SUPPLIED
FUSED DISCONNECT
CONDENSING
UNIT
FURNACE
COM
R
W
C
Y
R
G
GND
GND
FIELD 24-VOLT WIRING
FIELD 115-, 208/230-, 460-VOLT WIRING
FACTORY 24-VOLT WIRING
FACTORY 115-VOLT WIRING
Connect Y/Y2-terminal as shown for proper operation.
Some thermostats require a "C" terminal connection as shown.
If any of the original wire, as supplied, must be replaced, use
same type or equivalent wire.
208/230- OR
460-VOLT
THREE
PHASE
208/230-
VOLT
SINGLE
PHASE
WHT
BLK
WHT
BLK
W/W1
W2
Y/Y2
G
NOTES:
1.
2.
3.
A95236
For an explanation of status codes, refer to service label
located on control door or
Figure 14
, and the troubleshooting
guide which can be obtained from your distributor.
Retrieving Stored Fault Codes
NOTE
: Fault codes cannot be retrieved if a thermostat signal
(24-V on W, Y, G, etc.) is present, or if any delays such as
blower off-delays are active.
The stored status codes will NOT be erased from the control
memory when 115- or 24-V power is interrupted. See the
Service Label (See
Figure 14
) for more information. The most
recent fault code may be retrieved as follows:
1. Leave 115-V power connected to furnace.
2. Observe the status LED through the blower door (the
lower door on upflow applications) indicator. Refer to the
Service Label (See
Figure 14
) to interpret the LED.
3. Remove the Main/Control door (the upper door on upflow
installations).
4. BRIEFLY disconnect and reconnect ONE of the main
limit wires.
5. The LED will flash the last stored fault code. Refer to the
Service Label (See
Figure 14
) to interpret the LED.
6. A component test sequence will follow.
7. Reinstall the Main/Control door.
Component SelfTest
NOTE
: The furnace control component test allows all
components to run for a short time; except the gas valve and
humidifier terminal HUM are not energized. The EAC-1 terminal
is energized when the blower is energized. The HUM terminal
is energized when the inducer is energized. This feature helps
diagnose a system problem in case of a component failure.
The component test feature will not operate if any thermostat
signal is present at the control and not until all time delays are
completed.
To begin Component SelfTest:
1. Remove blower access door.
2. Disconnect the thermostat R lead from furnace control.
3. Manually close blower door switch.
Caution must be taken when manually closing this switch for
service purposes.
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal
injury, or death.
Blower access door switch opens 115V power to
control. No component operation can occur unless
switch is closed. Caution must be taken when
manually closing this switch for service purposes.
!
WARNING
4. For approximately 2 sec, short (jumper) the C terminal on
control to the TEST/TWIN 3/16—in. (5 mm)
quick-connect terminal on control until the LED goes off.
Remove jumper from terminals. (See
Figure 4
)
NOTE
: If TEST/TWIN and C terminals are jumpered longer
than 2 sec., LED will flash code 10 and ignore component test
request.
Component test sequence is as follows:
a. LED will display previous status code 4 times.
b. Inducer motor starts and continues to run until Step g
of component test sequence.
c. After 7 seconds the hot surface igniter is energized for
15 sec., then off.
d. Blower motor operates on LOHT speed for 10 sec.
e. Blower motor operates on HIHT speed for 10 sec.
f. Blower motor operates on COOL speed for 10 sec.
g.
I
nducer
motor
goes
to
low
s
p
eed
for
1
0
sec.
,
then
sto
p
s.
5. Reconnect R lead to furnace control, remove tape from
blower door switch, and re-install blower door.
6. Verify furnace shut down by lowering thermostat setting
below room temperature.
7. Verify that furnace restarts by raising thermostat setting
above room temperature.
8. Release blower door switch, reattach wire to “R” terminal
on furnace control board and replace blower door.
