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FURNACE TROUBLESHOOTING GUIDE
(COMBINATION HEATING AND COOLING UNITS WITH DIRECT SPARK IGNITION)
SET THERMOSTAT TO
CALL FOR HEAT
SET FAN SWITCH TO AUTO
START
WARNING
DISCONNECT POWER BEFORE
SERVICING.
SERVICE MUST BE BY A TRAINED,
QUALIFIED SERVICE TECHNICIAN.
HAZARDOUS VOLTAGE
LINE VOLTAGE CON-
NECTIONS
FLOW CHART CONTINUED ON NEXT PAGE
NO
YES
YES
YES
YES
NO
NO
NO
!
INDUCED DRAFT BLOWER
MOTOR STARTS
15 SECOND PREPURGE
REPLACE INTEGRATED
CONTROL BOARD (IFC)
REPLACE INDUCED
DRAFT BLOWER
NO
REPLACE NEGATIVE
PRESSURE SWITCH
REPLACE INTEGRATED
CONTROL BOARD (IFC)
IF WIRING IS OK
CHECK FOR EXHAUST,
INTAKE OR HEAT
EXCHANGER BLOCKAGE
AND RESET CONTROL
NO
REPLACE IGNITION CON-
TROL
YES
REPLACE VALVE
• CHECK LINE VOLTAGE TO CONTROL BOARD
• CHECK LOW VOLTAGE TRANSFORMER
• CHECK WIRING
• CHECK FOR 208-230 VAC TO IOM MOTOR
• CHECK IGNITOR CABLE
• CHECK SPARK IGNITOR POSITION AND CONDITION
• IS NEGATIVE PRESSURE SWITCH CLOSED?
• CHECK FOR OPEN ROLL-OUT CONTROL
• CHECK FOR OPEN LIMIT
• CHECK IGNITION CONTROL CHASSIS GROUND WIRE
• CHECK WIRING
• CHECK INLET GAS PRESSURE
• CHECK 24 VOLTS TO GAS VALVE
• CHECK FOR GAS FLOW TO AND FROM VALVE
• CHECK BURNER CARRYOVER
NOTE: THE SYSTEM WILL ATTEMPT TO LIGHT 3 TIMES WITH A 60 SECOND INTER-
PURGE BETWEEN TRIES. IF AFTER THE THIRD TIME THE BURNERS
DO NOT LIGHT, THE SYSTEM WILL LOCK OUT. IF THE UNIT IS EQUIPPED WITH
A UNITED TECH. OR JOHNSON CONTROLS IGNITION CONTROL, THE SYSTEM
WILL ATTEMPT TO LIGHT 3 TIMES EACH HOUR UNTIL THE BURNERS LIGHT OR
THE THERMOSTAT IS RESET.
YES
YES
IGNITOR SPARKS
MAIN BURNER LIGHTS
NO
• CHECK NEGATIVE PRESSURE
SWITCH SENSING TUBE
• CHECK FOR EXHAUST
BLOCKAGE
YES
YES
YES
REPLACE IGNITOR/
CABLE ASSEMBLY
REPLACE LIMIT
IF UNIT IS COLD
NO
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