46
I-SCE (09-18) PN207697R9
—Continued
Table 21. Troubleshooting Table
SYMPTOM PROBABLE CAUSE REMEDY
Pilot lights,
main valve
will not
open
1. Manual valve not open Open manual valve
2. Main valve not operating
a. Defective valve If 24-volt power is measured at valve connections and valve remains closed, replace
valve
b. Loose wire connections Check and tighten all wiring connections
3. Ignition control does not power main valve
a. Loose wire connections Check and tighten all wiring connections
b. Flame sensor grounded, pilot
lights, and spark continues
Ensure that flame sensor lead is not grounded and that insulation or ceramic is not
cracked; replace as required
c. Incorrect gas pressure Adjust gas pressure (refer to Gas Piping and Pressures)
d. Cracked ceramic at sensor Replace sensor
e. Faulty ignition controller If all checks listed in Spark Ignition System Maintenance indicate no other cause,
replace ignition controller; do not attempt to repair ignition controller, which has no
field-replaceable parts
Insufficient
heat with
heater
operating
1. Dirty filters in blower system Clean or replace filters
2. Incorrect manifold pressure Check manifold pressure (refer to Gas Piping and Pressures)
3. Limit control cycling on Check air throughput
4. Improper thermostat location or
adjustment
Refer to thermostat manufacturer’s instructions
5. Belt slipping on blower Adjust belt tension (refer to Belts, Blowers, and Drives)
6. Fan control improperly wired Ensure that wiring connections are in accordance with wiring diagram
7. Defective fan control Replace fan control
8. Blower set for too low temperature
rise
Decrease blower speed (refer to Belts, Blowers, and Drives) or increase static
pressure
Motor will
not run
1. Circuit open Check wiring and connections
2. Inoperative fan control Replace fan control
3. Fan control improperly wired Ensure that wiring connections are in accordance with wiring diagram
4. Inoperative contactor Replace contactor
5. Defective motor Replace motor
Motor
turns on
and off
while
operating
1. Motor overload device cycling Verify motor load against motor rating plate
Replace motor or overload device
2. 3-phase motor rotating in opposite
direction
Interchange two legs of supply connections
Motor cuts
out on
overload
1. Improper motor pulley adjustment Ensure that motor pulley is properly-adjusted (refer to Belts, Blowers, and Drives)
2. Improper static pressure on duct
system
Adjust dampers in duct system
3. Low voltage Check power supply
TROUBLESHOOTING—CONTINUED
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