Suburban SF-20F Service Manual

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The module board will then check for flame sense to verify successful lighting of the main burner flame. Sparking of the igniter is then
terminated. The gas valve and blower outputs will remain energized.
If ignition is successful the module board will monitor the flame sense, sail switch, and the limit switch circuits. The flame is sensed through
the spark wire and electrode therefore, it is essential that the electrode is properly positioned in the burner flame.
3 try Ignition Board
If the flame is NOT sensed after seven (7) seconds, or if the unit fails to ignite, a second fifteen (15) purge cycle will begin followed by
second trial for ignition sequence. After three (3) trial for ignition attempts with no ignition of the main burner, the module board will de-
energize the gas valve immediately and the blower will run for three (3) minutes and then go into lockout mode.
2
nd
Stage Heating
If during the thermostat cycle the demand for heat drops below the second stage thermostat setting ( 3 to 5 degrees variance depending
on thermostat manufacturer), the blower speed control board will be energized. The blower speed control board will energize the additional
gas valve solenoid and increase motor speed to the high position. Furnace will remain in the second stage operation until thermostat is
satisfied.
90 Second Shut Down
When the thermostat has reached its set point and the demand for heat ends, the gas valve will be de-energized and the flame will go
out. The post combustion purge period of 90 seconds begins. When it times out, the blower motor output is removed, and the blower
stops.
TROUBLE SHOOTING GUIDE SUBURBAN RV FURNACES
with TIME DELAY
12 VDC HEATING SECTION
Clean points, secure loose
-Yes-< connections, replace thermostat if
Anticipator is shorted.
? No
?
?
-Yes-<
Replace
thermostat.
Yes No
?
?-Yes-< Repair or replace connections
or parts with higher than normal amp draw.
? Yes
Check for 12vdc at furnace -No-< Check on/off switch on furnace
? Yes
?
Check fuse or circuit breaker -No-< Replace fuse/Reset breaker
? Yes
?
-No-< Replace the time delay relay.
? Yes
?
Yes -No-< Replace the
motor.
?
Check plug connection to the
-Yes-< mModule-electrode and wire-spark gap 1/8 inch between
probe and ground.
? No
?
Thermostat closes
-No-<
Check thermostat wire connections, contact
points and the heat anticipator.
Check 12vdc at blue wire, check the amp
draw to thermostat.
Check for shorts.
Check components amperage.
Approximately 10-20 seconds Blower is
operating
-No-<
Check for 12vdc at time delay relay and for
12vdc to red wire leading to the motor.
Check ground wire on terminal block.
After 15 seconds the module creates
spark and opens valve.
-No-<
Check for 12vdc between red and yellow
wires at the module board.

Suburban SF-20F Specifications

General

Brand	Suburban
Model	SF-20F
Category	Furnace
Language	English