035-17438-001 Rev. A (901)
22
Unitary Products Group
Cleaning the Heat Exchanger
Lower Heat Exchanger Access
1.
Turn off the electrical power to the unit and turn off gas
supply at the shutoff valve.
2.
Remove the blower and burner compartment access
doors. Disconnect the gas supply piping at the union to
permit removal of the entire burner and gas control
assembly from the vestibule panel. Use the wrench boss
on the gas valve when removing or installing this piping.
3.
Unplug the ignitor from the wire harness. Disconnect
sensor and rollout switch wires located on top of the air
shield. Identify and note the location of all leads for ease
of reinstallation. Also disconnect the wires at the side
rollout switches (upflow only) and the gas valve wires.
4.
Remove the screws holding the burner assembly to the
vestibule panel and remove this assembly. Handle the
assembly carefully since it contains the ignitor which is
fragile and easily broken. The lower portion of the heat
exchanger will now be exposed. To clean the burner
assembly, use a vacuum cleaner, or remove the burners
as outlined in burner cleaning, and clean in hot water.
Upper Heat Exchanger Access
1.
Perform steps 1 thru 4 above.
2.
Disconnect vent piping from the vent motor assembly at
the top panel on the furnace (upflow only). On downflow
installations this is not necessary.
3.
Unplug the ventor motor wires and ground wire. Remove
the pressure switch tubing at the tap on the ventor motor
housing.
NOTE:
It is recommended that replacement gaskets be
available before removing ventor motor.
4.
Remove six mounting screws that hold the ventor motor
to the restrictor plate. The surface is gasketed and gas-
ket can be reused if it is carefully removed. It is neces-
sary to remove this assembly to gain access to the
restrictor plate mounting holes. The ventor assembly
may be vacuumed if cleaning is necessary. If any vent
assembly parts are damaged, replace with an entire new
assembly (except for gaskets).
5.
Remove the perimeter screws attaching the restrictor
plate assembly to the vestibule panel. The surface is
also gasketed. The assembly, including the flue baffle
plate (rear) may be vacuumed or cleaned with hot water
if necessary.
6.
The upper portion of the heat exchanger is now accessi-
ble. With a long flexible wire brush, clean inside each
tube at both the top and bottom. The brush must pass
around the rear heat exchanger tubes. Vacuum loose
scale and dirt from each tube.
7.
Replace all components in reverse order. Regasket all
surfaces which required a gasket. Reconnect all wiring.
Reattach vent pipe and gas supply lines before restoring
service to furnace. Restore electrical power, check gas
supply piping for leaks, then verify furnace operation.
TROUBLESHOOTING
The following visual checks should be made before trouble-
shooting:
1.
Check to see that the power to the furnace and the igni-
tion control module is ON.
2.
The manual shutoff valves in the gas line to the furnace
must be open.
3.
Make sure all wiring connections are secure.
4.
Review the sequence of operation.
Start the system by setting the thermostat above the room
temperature. Observe the system's response. Then use the
troubleshooting section in this manual to check the system's
operation.
TROUBLESHOOTING THE BLOWER ASSEMBLY
Check to see that there is power to the furnace and the igni-
tion circuit module by turning the furnace power OFF for 5
seconds then ON. the red ignition control LED should light for
an instant then go out.
NO AIRFLOW OR MOTOR DOESN’T RUN
•
Verify that the blower wheel is properly tightened on the
motor shaft.
•
Verify 115 Volts AC at the power connector at the motor.
•
Be sure the connectors at the motor, ignition control and
CFM Selection Board are properly connected and fully
seated.
•
Switch the thermostat to CONTINUOUS FAN mode. If
the motor does not run, verify 24 VAC on the R to C
lines. If there is no voltage correct the cable/wiring, trans-
former fault. If there is voltage at the connector, the
motor has failed.
•
Check High Heat, Low Heat or Cool output terminals for
24 volts.
•
Check motor for tight shaft.
•
Perform Moisture Check. Be sure motor connectors are
facing down. Arrange the wire harness to create a drip
loop under the motor. Check for plugged condensate
drain. Check for low airflow. Check and plug leaks in
return ducts.
MOTOR ROCKS BUT WON’T START
•
Check for loose or compliant motor mount.
•
Perform motor/control replacement check.
