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SECTION II: SERVICE AND MAINTENANCE
MANUAL
SAFETY SECTION
The following safety rules must be followed when servicing the
furnace.
ELECTRIC SHOCK, FIRE OR EXPLOSION HAZARD
Failure to follow safety warnings exactly could result in
dangerous operation, serious injury, death or property
damage.
Improper servicing could result in dangerous operation,
serious injury, and death or property damage.
• Before servicing, disconnect all electrical power to the fur-
nace.
• When servicing controls, label all wires prior to discon-
necting. Reconnect wires correctly.
• Verify proper operation after servicing.
FURNACE MAINTENANCE SECTION
The furnace should be cleaned and adjusted by a certified dealer or
qualified service contractor once a year or before the start of every
heating season. The following items must be cleaned and serviced or
replaced if there are signs of deterioration.
1.
The vent terminal screen (if applicable).
2.
The furnace vent and combustion air intake passageways. Should
it be necessary to service the vent/air intake system, the manufac-
turer recommends this service be conducted by a qualified service
agency. The operation of this appliance requires the reassembly
and resealing of the vent/air intake system.
3.
The furnace burners, ignitor and flame sensor.
4.
The condensate collection and disposal system. If any disassem-
bly of components containing flue or vent gases is required, a
qualified service agency must perform the service.
FURNACE CLEANING SECTION
NOTE: The cleaning operations listed below must be performed only by
a qualified service agency.
Burner Removal/Cleaning
The main burners should be checked periodically for dirt accumulation.
If cleaning is required, follow this procedure:
1.
Turn off the electrical power to the unit.
2.
Turn off the gas supply at the external manual shut-off valve and
loosen the ground union joint.
3.
Remove the burner door and remove the burner box cover.
4.
Disconnect wires from flame sensor, rollout switch and HSI igniter.
Remove igniter carefully, as it is easily broken.
5.
Remove the screws that hold the burner box assembly to the vest
panel and remove the assembly.
6.
Remove burners from the burner assembly.
7.
Burners may be cleaned by rinsing in hot water.
8.
Reassemble the burners in the reverse order.
Cleaning the Heat Exchanger
1.
Turn off the electrical power to the unit.
2.
Turn off the gas supply at the external manual shut-off valve and
loosen the ground union joint.
3.
Remove the burner door and remove the burner box cover.
4.
Disconnect wires from flame sensor, rollout switch and HSI igniter.
Remove igniter carefully, as it is easily broken.
Unitary Products Group
5.
Remove the screws that hold the burner box assembly to the vest
panel and remove the assembly.
6.
Remove the vent pipe assembly, vent blower and condensate pan.
7.
The heat exchanger is now exposed.
8.
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. Then vacuum loose the scale and dirt from each
tube.
9.
Replace all components in reverse order. Reconnect all wiring.
10. Restore electrical power and gas supply to the furnace.
11. Check furnace operation.
Label all wires prior to disconnection when servicing
controls. Wiring errors can cause improper and danger-
ous operation. Verify proper operation after servicing.
Cleaning the Secondary Heat Exchanger
1.
Follow steps 1 - 7 under cleaning the Heat Exchanger.
2.
Remove the vent piping from the vent blower housing. Disconnect
the drain lines from the vent blower housing and from the conden-
sate drain pan. Remove the vent blower housing blower and the
condensate pan.
3.
Using a stiff wire brush, remove the loose scale or soot from each
tube.
4.
Vacuum the secondary heat exchanger.
5.
Finish the cleaning procedure by following steps 9 - 11 under
cleaning the Heat Exchanger.
Cleaning the Vent / Air Intake System
Should it be necessary to service the vent / air intake system, the man-
ufacturer recommends this service be conducted by a qualified service
agency.
The operation of this appliance requires the reassembly and resealing
of the vent / air intake system as specified in the "Combustion Air and
Vent System" located in the Installation Manual.
SEQUENCE OF OPERATION
The following describes the sequence of operation of the furnace. Refer
to Figure 1 for component location.
1.
Call for 1st stage only
• On a call for 1st stage heat, the thermostat closes a circuit
between R and W1.
• The Microprocessor in the Furnace Control runs a 'Self Check'.
• The Control checks the Primary Limit, Auxiliary Limit, and Roll-
out Switches for closed contacts.
• The Control checks that the Low Fire Pressure Switch (1LP) is
open.
• The Inducer Motor is energized on high speed, closing the con-
tacts of 1LP.
• The Control checks that 1LP is closed.
• The Igniter is energized for 17 seconds.
• The Gas Valve is energized on 1st Stage (Low Fire).
• Flame Rectification is recognized within 7 seconds.
• The Inducer is switched to low speed.
• 30 seconds after flame is proven, the 'Heat Low' relay is ener-
gized providing 120 Volts AC to the Blower Motor.
• At the same time, the EAC and Hum relays are energized, pro-
viding 120 Volts AC to the EAC Hot and Hum terminals.
271042-UUM-A-0407
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