29
SERVICING
WARNING
Line Voltage now present.
1.
Check for 120 volts from Line 1 (Hot) to Line 2 (Neu
-
tral) at the ignition control. No voltage, check the door
switch connections and wire harness for continuity.
2.
Check for 24 volts from W to C terminal on the
ignition control. No voltage. Check transformer, room
thermostat, and wiring.
If you have 24 volts coming off the transformer but
receive approximately 13 volts on the terminal board
between (C) and (R), check for blown fuse.
3.
Check for 120 volts to the induced draft blower by
measuring voltage between Pin 1 (on the 2-pin con-
nector) and Line (Neutral) on the control board. No
voltage, replace ignition control.
4.
If voltage is present in Steps 1 through 3 and the
induced draft blower is operating, check for 120 volts
to the ignitor during the preheat cycle. Measure volt-
age between Pin 2 (on the 2-pin connector) and Line
(Neutral) on the control board. No voltage, check
pressure switch.
5.
After the ignitor warmup time, begin checking for 24
volts to the gas valve. Voltage will be present for seven
seconds only if proof of flame has been established.
S-314 CHECKING FLAME SENSOR
A flame sensing device is used in conjunction with the igni
-
tion control module to prove combustion. If proof of flame is
not present the control will de-energize the gas valve and
“retry” for ignition or lockout.
The following drawings illustrate from a bottom view, the ap
-
proximate distances for the ignitor and flame sensor to the
gas in shot burner. You will note they are in the main burner
stream, not in the carry over ports as shown in the following
figure.
Flame Sensor
Models with Integrated Ignition
Control & Flame Sensor Probe
(80% Upflow Model Shown, Counterflow Similar)
WARNING
HIGH VOLTAGE
Disconnect ALL power before servicing or in
-
stalling this unit. Multiple power sources may
be present. Failure to do so may cause proper
-
ty damage, personal injury or death.
1.
Disconnect the blue flame sensor wire from the
sensor.
2. Connect a micro-amp meter in series with this wire
and the sensor terminal.
3. Place the unit into a heating cycle.
WARNING
Line Voltage now present.
4.
As soon as flame is established a micro-amp reading
should be evident once proof of flame (micro-amp
reading) is established, the hot surface ignitor will be
de-energized.
5. The Integrated Ignition controls will have 1 to 4 mi-
cro-amps. If the micro-amp reading is less than the
minimum specified, check for high resistance wiring
connections, sensor to burner gap, dirty flame sen
-
sor, or poor grounding.
6.
If absolutely no reading, check for continuity on all
components and if good - replace ignition control
module.
NOTE: Contaminated fuel or combustion air can cre
-
ate a nearly invisible coating on the flame sensor.
This coating works as an insulator causing a loss in
the flame sense signal. If this situation occurs the
flame sensor must be cleaned with steel wool.
