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SERVICE AND TECHNICAL SUPPORT MANUAL
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.
!
WARNING
FIRE HAZARD
Failure to follow this warning could result in personal injury,
death, and/or property damage.
Reinstall manifold pressure tap plug in gas valve to
prevent gas leak.
CAUTION
!
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
midïpoint of rise range or slightly above.
Adjust Thermostat Heat Anticipator
When using a nonïelectronic thermostat, the thermostat heat
anticipator must be set to match the amp draw of the electrical
components in RïW circuit. Accurate amp draw readings can
be obtained at the thermostat subbase terminals R and W.
Figure 5 illustrates the easy method of obtaining actual amp
draw. The amp reading should be taken after blower motor has
started and furnace is heating. Connect ammeter wires as
shown in Figure 5. The thermostat anticipator should not be in
the circuit while measuring current.
subbase, the thermostat must be disconnected from R and W
wires
during
current
measurement.
manufacturer's instructions for adjusting heat anticipator and for
varying heating cycle length. For an electronic thermostat, set
cycle rate for 3 cycles per hour.
Figure 5
Amp. Draw Check with Ammeter
THERMOSTAT SUBBASE
TERMINALS WITH
THERMOSTAT REMOVED
(ANITICIPATOR, CLOCK, ETC.,
MUST BE OUT OF CIRCUIT.)
R Y W G
10 TURNS
FROM UNIT 24ïV
CONTROL TERMINALS
5.0 AMPS ON AMMETER
EXAMPLE:
10 TURNS AROUND JAWS
10
If thermostat has no
See
thermostat
HOOKïAROUND
AMMETER
=
A96316
Specifications subject to change without notice.
Check Safety Controls
The flame sensor, gas valve, and pressure switch were all
checked in the Startïup procedure section as part of normal
operation.
1. Check Main Limit Switch
This control shuts off combustion system and energizes
airïcirculating blower motor, if furnace overheats. By
using this method to check limit control, it can be
established that limit is functioning properly and will
operate if there is a restricted returnïair supply or motor
failure. If limit control does not function during this test,
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 reïlight when furnace cools down.
2. Check Pressure Switch(es)
This control proves operation of the draft inducer blower.
a. Turn off 115ïV power to furnace.
b. Disconnect inducer motor lead wires from wire
harness.
c. Turn on 115ïV power to furnace.
d. Set thermostat to "call for heat" and wait 1 minute.
When 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 pressure switch did not function
properly and correct condition.
f. Turn off 115ïV power to furnace.
g. Reconnect inducer motor wires, replace outer door,
and turn on 115ïV power.
h. Blower will run for 90 seconds before beginning the
call for heat again.
i. Furnace should ignite normally.
Checklist
1. Put away tools and instruments. Clean up debris.
2. Verify that the jumper is removed from the TEST/TWIN
terminal. Verify that there is nothing plugged into the PLT
connector.
NOTE: Note: If there is a jumper connector plugged into PLT,
remove it and discard. (See Figure 4)
3. Verify that (TT) switch SW-1 is set properly.
Figure 4)
4. Verify that the Heat OffïDelay SWï2 and SWï3 switches
are set as desired. (See Figure 4)
5. Verify that the blower and control ("Main") doors are
properly installed.
6. Verify that the Status LED glows. If not, check that the
power supply is energized and that the blower door is
secure. (See Figure 14) to interpret diagnostic codes.
7. Cycle test furnace with room thermostat to be sure that it
operates properly with the room thermostat. Check all
modes including Heat, Cool and Fan.
8. Check operation of accessories per manufacturer's
instructions.
9. Review Home Owner's Information with owner.
10. Attach entire literature packet to furnace.
Gas Furnace: (F/G)9MXT
(See
440 04 4321 02
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