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035-19671-001 Rev. A (0404)

Unitary Products Group

7

Hot Surface Ignition System

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 upper access panel 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

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. Dis-
connect 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. See Figure 4.

3.

Unplug the igniter 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 discon-
nect 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 igniter, 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 burn-
ers as outlined in burner cleaning, and clean in hot water.

Upper Heat Exchanger Access

1.

Perform steps 1-4 above.

2.

Disconnect vent piping from the vent motor assembly at the top
panel on the furnace (upflow only). On downflow models, the vent
pipe is attached to the vent motor out-let. Remove this screw
before proceeding.

3.

Unplug the vent motor wires and ground wire. Remove the pres-
sure switch tubing at the tap on the vent motor housing.

NOTE: 

It is recommended that replacement gaskets be avail-able

before removing vent motor.

1.

Remove six mounting screws that hold the vent motor to the
restrictor plate. The surface is gasketed and gasket can be reused
if it is carefully removed. It is necessary to remove this assembly to
gain access to the restrictor plate mounting holes. The assembly
may be vacuumed if cleaning is necessary. If any vent assembly
parts are damaged, replace with an entire new assembly (except
for gaskets).

2.

Remove the perimeter screws attaching the restrictor plate assem-
bly 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.

3.

The upper portion of the heat exchanger is now accessible. 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.

4.

Clean - Replace all components in reverse order. Re-gasket 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, and
then verify furnace operation.

TROUBLESHOOTING

The following visual checks should be made before troubleshooting:

1.

Check to see that the power to the furnace and the ignition control
module is ON.

2.

The manual shut-off 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.

TABLE 2: 

Replacement PSC Motor / Capacitor Information

High Fire Inputs

Airflow

Cabinet Size

Motor 

Part Number

Motor 

Horsepower

Capacitor 

Part Number

Capacitor 

Rating 

BTU/H (kW)

CFM (m³)

60,000 (17.6)

1,200 (33.98)

B

024-23271-000

1/2

024-20045-000

7.5 f

80,000 (23.4)

1,600 (45.31)

C

024-26002-000

3/4

024-20046-000

10.0 f

100,000 (29.3)

2,000 (56.63)

C

024-23288-001

1.0

024-20446-000

15.0 f

120,000 (35.1)

2,000 (56.63)

D

024-23238-001

1.0

024-20446-000

15.0 f

HOT SURFACE IGNITION SYSTEM
Do not attempt to light this furnace by hand (with a
match or any other means). There may be a potential
shock hazard from the components of the hot surface
ignition system. The furnace can only be lit automatically
by its hot surface ignition system.

Label all wires prior to disconnection when servicing
controls. Wiring errors can cause improper and danger-
ous operation. Verify proper operation after servicing.

Summary of Contents for G8D-UH

Page 1: ...electrical parts that have been wet or the furnace if deemed necessary FIRE OR EXPLOSION HAZARD Failure to follow safety warnings exactly could result in serious injury death or prop erty damage Do not store or use gasoline or other flammable vapors and liquids in the vicinity of this or any other appliance WHAT TO DO IF YOU SMELL GAS Do not try to light any appliance Do not touch any electrical s...

Page 2: ...space containing the furnace 4 Examine the furnace casing making sure the physical support is sound without sagging cracks or gaps Examine the furnace base making sure it is physically sound without cracks gaps or sagging and has a good seal 5 Examine the furnace casing for obvious signs of deterioration 6 Examine the burner flames to make sure they are in good adjust ment Refer to the pictorial s...

Page 3: ...part of the control system and any gas control which has been under water Operating Instructions 1 STOP Read the safety information above 2 Set the thermostat to the lowest setting 3 Turn off all electric power to the appliance 4 Remove burner door 5 Move gas control switch to the OFF position Do not force See Figure 4 6 Wait five 5 minutes to clear out any gas If you then smell gas STOP Follow B ...

Page 4: ...ters by using brackets with the number two 2 D If the air filters are on both sides of the furnace then you have a two sided return You must replace both air filters Table 1 will indicate 2 filters by using brackets with the number two 2 3 After you determine the cabinet size and what return configuration you have look up the recommended filter size from Table 1 Removing Filters Internally Mounted...

Page 5: ...en using a 2 Stage thermostat the Timer should be discon nected The Inducer Motor is shifted to high speed by the control closing the contacts of 2LP The High Fire Pressure Switch The Control checks that 2LP is closed The Gas Valve is energized on 2nd Stage High Fire The Control simultaneously de energizes the Heat Low relay and energizes the Heat High relay providing 120 Volts AC to a different s...

Page 6: ...ess doors 2 Remove blower assembly mounting screws and slide the blower assembly out of the slots in the deck If the two shipping screws were not previously removed also remove and discard these two screws located on each front corner of the blower assembly 3 Loosen the blower wheel set screw that secures the blower wheel to the blower motor shaft 4 Remove the motor mount bolts 5 Slide the variabl...

Page 7: ...placement gaskets be avail able before removing vent motor 1 Remove six mounting screws that hold the vent motor to the restrictor plate The surface is gasketed and gasket can be reused if it is carefully removed It is necessary to remove this assembly to gain access to the restrictor plate mounting holes The assembly may be vacuumed if cleaning is necessary If any vent assembly parts are damaged ...

Page 8: ...Dirty Filter Improperly sized duct system Incorrect blower speed selection Incorrect firing rate Faulty blower motor Faulty Control 6 Flash Reason 1LP has opened five times during one call for heat Effect Control enters Soft Lockout It will automatically reset and try again after 1 hour Causes Restricted vent system Vent system that exceeds specifications High wind 7 Flash Reason Flame rectificati...

Page 9: ...OW INDUCER LOW STAGE PRESSURE SWITCH HSI 1ST STAGE MAIN VALVE FLAME SENSE LOW CIRCULATOR HEAT SPEED 1ST STAGE LOW PRESSURE SWITCH CLOSE RECOGNITION HSI WARM UP 17 SEC IGNITION ACTIVATION PERIOD 4 SEC TRIAL FOR IGNITION 7 SEC INTER PURGE 60 SEC HSI WARM UP 27 SEC IGNITION DEACTIVATION PERIOD 3 SEC HEAT FAN DELAY ON 30 SEC BURN TIME POST PURGE 15 SEC HEAT FAN DELAY OFF SELECTABLE 60 90 120 180 SEC O...

Page 10: ...035 19671 001 Rev A 0404 10 Unitary Products Group SECTION III REPLACEMENT PARTS LIST 28 38 39 32 27 3 30 26 5 10 9 22 24 6 20 11 2 37 29 8 23 12 7 35 17 19 21 13 1 16 15 25 4 41 12A 7 35 24 36 12 19 11 ...

Page 11: ...N GAS 20 BRACKET IGNITER 21 DECK BLOWER Rear 22 DECK FRONT 23 HEAT EXCHANGER ASS Y 24 MANIFOLD GAS 25 PANEL ACCESS BURNERS 26 PAN BASE 27 PANEL FRONT Blower 28 PANEL TOP 29 WRAPPER INSULATED 30 CHANNEL TOE PLATE 31 FILTER 32 PLUG WINDOW CLEAR 875 33 RETAINER FILTER 34 CLIP SPRING FILTER RETAINER 35 BRACKET ROLL OUT SWITCH MISCELLANEOUS 36 ORIFICE BURNER Natural 45 37 PLATE RESTRICTOR N Model PLATE...

Page 12: ...stage Heat One Stage Cool ALL MODELS 2TB17700424 THERMOSTAT Subbase for 2TH13700424 ALL MODELS 2ET07700324 THERMOSTAT Programmable ALL MODELS 2ET07700224 THERMOSTAT Deluxe Programmable One stage Heat One stage Cool with subbase ALL MODELS REPLACEMENT PART CONTACT INFORMATION This is a generic parts list To request a complete parts list refer to the contact information below Visit our website at ww...

Page 13: ...035 19671 001 Rev A 0404 Unitary Products Group 13 SECTION IV WIRING DIAGRAM FIGURE 9 Wiring Diagram ...

Page 14: ...035 19671 001 Rev A 0404 14 Unitary Products Group NOTES ...

Page 15: ...035 19671 001 Rev A 0404 Unitary Products Group 15 ...

Page 16: ...applies only to products installed in the United States and Canada EXCLUSIONS This warranty does not cover any 1 Shipping labor or material charges 2 Damages resulting from transportation installation or servicing 3 Damages resulting from accident abuse fire flood alteration or acts of God tampering altering defacing or removing the product serial number will serve to void this warranty 4 Damages ...

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