16
Service Guide For Furnaces with PGB
Power Burner with Direct Ignition
Burner motor does not run - thermostat calls for heat
1. Defective thermostat circuit - bridge TT connections on
burner junction box, if burner motor runs, check:
a. Thermostat connections
b. Thermostat
2. No voltage to burner - plug test lamp into burner plug
receptacle, if it does not light, check for:
a. Blown fuse, electric supply off
b. Door switch not making contact
c. Limit switch in open mode
d. Check for clean air filter and proper airflow
e. Loose wire connections
f.
Check for tripped manual reset auxiliary limit.
3. 120 volts is available to burner - Test lamp does not light.
Remove junction box cover on burner, check for:
a. Loose wires
b. Defective transformer
c. Defective motor
Burner motor does not run, no main flame
1. Defective centrifugal switch
a. Check the operation of centrifugal switch by removing
end bell of the burner motor.
b. If the contacts are accessible, clean them.
c. If the contacts are accessible, replace motor as on
some burner motors the centrifugal switch cannot
be replaced.
2. Burner in purge mode - allow 3 minutes for burner to
establish flame.
3. Check for proper electrical connections at purge timer,
control box or gas valve.
4. Check for gas supply - gas line valve on, control lever on.
5. Check for burner safety lockout. (Restart burner)
6. Check for 24 volts to ignition control
a. No voltage at purge timer - check the centrifugal
switch in the combustion motor.
b. No voltage to ignition control - check purge timer
(allow one minute for purge timer to activate).
c. Check for 120 volts to ignition control. (-Voltmeter
at L1 and L2).
1. Remove AMP plug from burner tube receptacle and
check for 120 volts at the plug during ignition sequence
(allow 3 minutes for ignition cycle).
2. Replace ignition control if 120 volts is not supplied to
AMP plug within 3 minutes of ignition cycle start.
120 volts is available at AMP plug
Ignitor does not heat up
1. Disconnect burner plug from furnace receptacle.
2. Disconnect AMP plug from burner tube receptacle and
check ignitor circuit through receptacle with an ohmmeter.
a. Normal ohm reading should be 40 to 75 ohms.
b. An infinite or zero ohm reading indicates a defective
ignitor and it must be replaced.
3. Check for continuity from ignitor receptacle to burner
ground.
4. Check for hairline cracks in ignitor’s insulating ceramic.
Main flame ignites but burner locks out
1. Ignition control is not properly grounded.
2. Defective ignition control.
3. Improper gas pressure or burner air adjustment is not
allowing flame to contact ignitor tip for flame proving
rectification.
Ignition control is powered (120v and 24v).
Ignitor does not heat up
When replacing the ignition control, replacement
control MUST have the safety lockout time.
FAILURE TO FOLLOW THIS WARNING MAY
RESULT IN AN EXPLOSION.
WARNING:
!
1. Always disconnect power before servicing.
2. Only persons trained and experienced in
direct ignition systems should service this
equipment.
3. If a condition exists that causes the ignition
control to go into safety lockout, meter
readings must be taken quickly after restart
- within trial for ignition period.
4. Always de-energize the system for at least 45
seconds before recycling for further tests.
5. The ignition control cannot be repaired. If
the troubleshooting procedure indicates a
malfunction in the control, it must be replaced.
IMPORTANT:
!
