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FASCO COMBUSTION FAN ENDSWITCH
1. The Fasco 115 volt motor is equipped with a centrifugal endswitch. The purpose of the endswitch is to ensure that the
combustion fan motor has reached the proper operating RPM which is generally about 3400 rpm. If the endswitch fails to
close then the 24 volt circuit to the gas primary is interrupted and the gas valve will not open. If the Blower motor has 115
volts applied but is not rotating then the motor assembly must be replaced. Lastly if the motor is not rotating, the centrifugal
switch will not make and 24 volts will not be present at the gas primary control.
IGNITER ROD
1. The igniter rod is responsible for conveying the spark to a grounding rod in an appropriate location to ignite the gas and air
mix. The igniter Rod gap should be 1/8" Larger Gaps will create ignition problems. If the igniter rod is cracked, a sparking
sound will be heard inside the burner airtube but ignition will not occur and lockout will occur.
RECTIFICATION ROD
The Rectification Rod is responsible for sending a DC signal back to the control to tell the control that a flame is present. A typical
flame signal strength ranges from 2 to 5 micro amps and should be stable. If the rectification rod is cracked, then the signal will be
grounded thus no current back to the control causing lockout
THERMOSTAT CALLS FOR HEAT AND THE FOLLOWING CONDITIONS OCCUR:
1. PROBLEM: The Combustion Fan motor is not operating.
POSSIBLE REASONS:
A. Power is not on.
B. Circuit Breaker tripped
C. Thermostat in the off position
D. Thermostat connections to T-T terminals on junction box have shorted to the junction box.
E. Bad Thermostat
F. Blower wheel Jammed
G. Excessive amount of debris stuck in blower wheel blades.
H. 24 volt transformer is not functioning properly.
I. Thermostat leads not connected to the T-T terminals.
J. Motor shorted out due to over voltage
2 PROBLEM: Combustion Fan motor runs but ignition sequence does not occur.
POSSIBLE REASONS
A. Blower Motor Endswitch not closed which completes the 24 volt circuit to the Gas primary
B. The Blower motor is not reaching full rpm due to debris on wheel
C. Low Voltage to the Blower Motor
D. Loose Connections on the 24 volt circuit after the endswitch or between Fan relay and the 24 volt side of the gas primary
E. The S87K Gas Primary control is defective and must be replaced.
3. PROBLEM: Combustion Fan motor runs and Ignition Sequence initiated but goes Into Lockout.
POSSIBLE REASONS
A. Flame Sensing Rod is cracked which would ground out the signal.
B. Spark Electrode Rod is cracked shorting the spark to ground.
C. Loose Connection on Flame Sensing Rod
D. Loose Connection on Spark Electrode Rod
E. Gas Primary Control not allowing 24 volts to Gas Valve
F. Gas Valve shorted out or defective
G. No Earth Ground between burner and appliance.
H. Flame Sensing Rod grounding out on Burner
1. Spark Electrode location shifted
J. Gas Primary Control not generating spark
K. Ignition Wire insulation melted and is grounding out on burner
L. Gas Supply is not turned on
M.Gas Manifold pressure too high
N.Gas Manifold -pressure too low
0.High negative draft conditions
P.Flue Passage is blocked
Q.Gas Supply line is undersized
R.Multi appliances operating on undersized line
S.Insufficent combustion air flow
T.Incorrect Air shutter adjustment allowing too much combustion air to enter burner.
