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e. Remove blower wheel from housing.
f. Clean wheel and housing.
12. Reassemble motor and blower by reversing steps 11f, finish-
ing with 11a. Be sure to reattach ground wire to the blower
housing.
13. Verify that blower wheel is centered in blower housing and set
screw contacts the flat portion of the motor shaft. Loosen set
screw on blower wheel and reposition if necessary.
14. Spin the blower wheel by hand to verify that the wheel does
not rub on the housing.
15. Reinstall blower assembly in furnace.
16. Reinstall control box assembly in furnace.
Heating fan speed(s) MUST be adjusted to provide proper air
temperature rise as specified on the rating plate. Failure to
adjust the heating speed(s) may shorten heat exchanger life.
Recommended operation is at the midpoint of the rise range
or slightly above. Refer to ″SET TEMPERATURE RISE″
under START-UP, ADJUSTMENT, and SAFETY CHECK.
NOTE: Refer to Table 7 for motor speed lead relocation if leads
were not identified before disconnection.
17. Reconnect blower leads to furnace control. Refer to furnace
wiring diagram, and connect thermostat leads if previously
disconnected. (See Fig. 39.)
18. To check blower for proper rotation:
a. Turn on electrical supply.
Blower access door switch opens 115-v power to furnace
control. No component operation can occur. Caution must be
taken when manually closing this switch for service purposes.
Failure to follow this warning could result in electrical shock,
personal injury, or death.
b. Manually close blower access door switch.
NOTE: If thermostat terminals are jumpered at the time blower
access door switch is closed, blower will run for 90 sec before
beginning a heating or cooling cycle.
c. Perform component self-test as shown at the bottom of the
SERVICE label, located on the front of blower access door.
d. Verify blower is rotating in the correct direction.
19. If furnace is operating properly, RELEASE BLOWER AC-
CESS DOOR SWITCH. Replace blower access door and
remove any jumpers or reconnect any disconnected thermostat
leads.
20. Downflow or horizontal furnaces with vent pipe through
furnace only:
a. Install and connect short piece of vent pipe inside furnace
to existing vent.
b. Connect vent connector to vent elbow.
21. Reinstall casing door.
22. Turn on gas supply and cycle furnace through one complete
heating and cooling cycle. Verify the unit temperature rise as
shown in Adjustments Section. Adjust temperature rise as
shown in Adjustments Section. If outdoor temperature is
below 70° F, turn off circuit breaker to outdoor unit before
running furnace in the cooling cycle. Turn outdoor circuit
breaker on after completing cooling cycle.
CLEANING HEAT EXCHANGER
The following steps should be performed by a qualified service
technician:
NOTE: If the heat exchangers get a heavy accumulation of soot
and carbon, they should be replaced rather than trying to clean
them thoroughly. A build-up of soot and carbon indicates that a
problem exists which needs to be corrected, such as improper
adjustment of manifold pressure, insufficient or poor quality
combustion air, incorrect size or damaged manifold orifice(s),
improper gas, or a restricted heat exchanger. Action must be taken
to correct the problem.
If it becomes necessary to clean the heat exchangers because of
dust or corrosion, proceed as follows:
1. Turn OFF gas and electrical power to furnace.
2. Remove outer access door.
3. Disconnect vent connector from furnace vent elbow.
4. For downflow or horizontal furnace having an internal vent
pipe, remove internal vent pipe within the casing.
5. Disconnect wires to the following components. Mark wires to
aid in reconnection of:
a. Draft safeguard switch.
b. Inducer motor.
c. Pressure switch(es).
d. Limit overtemperature switch.
e. Gas valve.
f. Hot surface igniter.
g. Flame-sensing electrode
h. Flame rollout switches.
i. Remove NOx baffles on low NOx models.
6. Remove screws that fasten the collector box assembly to the
cell panel. Be careful not to damage the collector box. Inducer
assembly and elbow need not be removed from collector box.
7. Disconnect gas line from gas manifold.
8. Remove the 4 screws that attach the burner assembly to the
cell panel. The gas valve and individual burners need not be
removed from support assembly.
NOTE: Be very careful when removing burner assembly to avoid
breaking igniter. See Fig. 44 and 45 for correct igniter location.
Fig. 44—Position of Igniter to Burner
A02150
9/32”
11/32”
33