43
FIGURE 20
FURNACE TROUBLESHOOTING GUIDE
(COMBINATION HEATING AND COOLING UNITS WITH DIRECT SPARK IGNITION)
SET THERMOSTAT TO
CALL FOR HEAT
S
ET FAN SWITCH TO AUTO
S
TART
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
N
O
YES
YES
YES
YES
NO
NO
NO
!
I
NDUCED DRAFT BLOWER
MOTOR STARTS
30 SECOND PREPURGE
R
EPLACE INTEGRATED
CONTROL BOARD (IFC)
R
EPLACE 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 IFC
• CHECK LOW VOLTAGE TRANSFORMER
•
CHECK WIRING
•
CHECK FOR 208-230 VAC TO IDM MOTOR
• CHECK IGNITOR CABLE
• CHECK SPARK IGNITOR POSITION AND CONDITION
• IS EACH NEGATIVE PRESSURE SWITCH CLOSED?
• CHECK FOR OPEN ROLL-OUT CONTROLS
• 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 4 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. THE SYSTEM WILL ATTEMPT TO LIGHT 4 TIMES EACH HOUR
UNTIL THE BURNERS LIGHT OR THE THERMOSTAT IS RESET OR POWER IS
REMOVED FOR 3 SECONDS OR GREATER.
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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