SERVICE AND TECHNICAL SUPPORT MANUAL
Gas Furnace: (F/G)9MXE
Specifications subject to change without notice.
440 04 4311 08
11
Change the blower speed taps as required to maintain proper
temperature rise for Heating and Cooling as described above.
To change blower motor speed selections for heating mode,
remove blower motor lead from control HEAT terminal(s). (See
Figure 4
) Select desired blower motor speed lead(s) from the
other motor leads and relocate it/them to HEAT (heating blower
tap) terminal(s). Reconnect original lead on SPARE terminal.
Adjust Blower Off Delay (Heat Mode)
If desired, the main blower off time delay period may be
lengthened or shortened when operating in the heating mode
to provide greater comfort. For position and location of jumpers
on control center. (See
Figure 4
and
Figure 15
)
The blower off-delay has four adjustable settings from 90 sec to
180 sec. (See
Table 4
) To change the blower off delay setting,
move the jumper from one set of pins on the control to the pins
used for the desired blower off delay. Factory blower off-delay
setting is 120 sec.
Table 4
Blower Off Delay Jumper Positions
PINS
1 AND 2
2 AND 3
3 AND 4
4 AND 5
Time (in sec.)
90
120
150
180
Adjust Cooling Airflow
The cooling airflow can be set from the remaining blower speed
taps. Refer to the Air Delivery Tables in these instructions.
If a two
−
stage air conditioning or heat pump is installed, the
Low Cooling Speed is the same speed tap as the Continuous
Fan speed (FAN).
Adjust Continuous Fan Airflow
The Continuous Fan airflow can be set from the remaining
blower speed taps. Refer to the Air Delivery Tables in these
instructions.
The Continuous Fan speed can be changed to any other
speed tap by toggling the Fan switch at the thermostat. See the
Sequence of Operation for details.
FURNACE OVERHEATING HAZARD
Failure to follow this caution may result in reduced furnace
life.
Recheck temperature rise. It must be within limits specified
on the rating plate. Recommended operation is at the
mid--point of rise range or slightly above.
CAUTION
!
Adjust Thermostat Heat Anticipator
Mechanical thermostat:
Set thermostat heat anticipator to
match the amp. draw of the electrical components in the R--W
circuit. Accurate amp. draw readings can be obtained at the
wires normally connected to thermostat sub-base terminals, R
and W. The thermostat anticipator should NOT be in the circuit
while measuring current.
1. Remove thermostat from sub-base or from wall.
2. Connect an amp. meter across the R and W sub-base
terminals or R and W wires at wall.
3. Record amp. draw across terminals when furnace is in
low heat and after blower starts.
4. Set heat anticipator on thermostat per thermostat
instructions and install on sub-base or wall.
5. Install blower access door.
Electronic thermostat:
Set cycle rate for 3 cycles per hr.
Figure 5
Amp. Draw Check with Ammeter
A96316
R Y W G
10 TURNS
THERMOSTAT SUBBASE
TERMINALS WITH
THERMOSTAT REMOVED
(ANITICIPATOR, CLOCK, ETC.,
MUST BE OUT OF CIRCUIT.)
HOOK-AROUND
AMMETER
EXAMPLE: 5.0 AMPS ON AMMETER
10 TURNS AROUND JAWS
= 0.5 AMPS FOR THERMOSTAT
ANTICIPATOR SETTING
FROM UNIT 24-V
CONTROL TERMINALS
Check Safety Controls
The flame sensor, gas valve, and pressure switch were all
checked in the Start
−
up procedure section as part of normal
operation.
1. Check Main Limit Switch
This control shuts off combustion system and energizes
air
−
circulating blower motor, if furnace overheats. By
using this method to check the temperature limit control,
it can be established that the limit is functioning properly
and that the limit will operate if there is a restricted
return
−
air supply or motor failure. If the limit control does
not function during this test, the cause must be
determined and corrected.
a. Run furnace for at least 5 minutes.
b. Gradually block off return air with a piece of
cardboard or sheet metal until the limit trips.
c. Unblock return air to permit normal circulation.
d. Burners will re
−
light when furnace cools down.
2. Check Pressure Switch(es)
This control proves operation of the draft inducer blower.
a. Turn off 115
−
v power to furnace.
b. Disconnect inducer motor lead wires from wire
harness.
c. Turn on 115
−
v power to furnace.
d. Set thermostat to “call for heat” and wait 1 minute.
When low pressure switch is functioning properly, hot
surface igniter should
NOT
glow and control
diagnostic light flashes a status code 3. If hot surface
igniter glows when inducer motor is disconnected,
shut down furnace immediately.
e. Determine reason low pressure switch did not
function properly and correct condition.
f. Turn off 115
−
v power to furnace.
g. Reconnect inducer motor wires, replace door, and
turn on 115
−
v power.
h. Blower will run for 90 seconds before beginning the
call for heat again.
i. Furnace should ignite normally.
