128
SERVICING
6. If proof of flame was established voltage will be provided
to the air circulation blower following the heat on delay
period.
a. BEFORE replacing the ECM motor assembly or the
end bell, first check the motor with a GE TECMate
PRO tester. If the motor runs with the tester, the
motor is good. To check the end bell, see the previ-
ous variable speed testing section of this manual be-
fore replacing the end bell.
b. The two-stage variable speed furnaces should have
120 Volts at the motor at all times, even without a call
for cooling or heating. These motors receive their op-
erational signals (24 Volts) through the 16-pin wiring
harness, connected between the motor and integrated
control board. NOTE: For complete troubleshooting
information on units using the ECM/ICM blower mo-
tors, refer to the servicing section - Checking Air Cir-
culator Blowers (S-16B and S-16C) in this service
manual.
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 inshot 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)
3/16" + 1/16"
DISTANCE OF
IGNITOR TO BURNER
DISTANCE OF
SENSOR TO BURNER
23/64"
+ 1/64"
FLAME SENSOR
IGNITOR
BURNERS
Models with Integrated Ignition
Control & Flame Sensor Probe
(90% Upflow Model Shown, Counterflow Similar)
WARNING
HIGH VOLTAGE
D
ISCONNECT ALL POWER BEFORE SERVICING OR
INSTALLING THIS UNIT.
MULTIPLE POWER SOURCES MAY
BE PRESENT.
FAILURE TO DO SO MAY CAUSE PROPERTY
DAMAGE, PERSONAL INJURY OR DEATH.
1. On all 80% models disconnect the orange flame sensor
wire from the sensor or on all 90% models 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. Be sure the positive side of the meter is to Orange or
Blue wire (depending on the model) and the negative
side of the meter is to sensor terminal.
L
INE VOLTAGE NOW PRESENT
WARNING
4. Place the unit into a heating cycle.
5. As soon as flame is established a micro-amp reading
should be evident once proof of flame (micro-amp read-
ing) is established, the hot surface ignitor will be de-
energized.
6. The Integrated Ignition controls will have 1 to 4 micro-
amps. If the micro-amp reading is less than the mini-
mum specified, check for high resistance wiring con-
nections, sensor to burner gap, dirty flame sensor, or
poor grounding.
7. If absolutely no reading, check for continuity on all com-
ponents and if good - replace ignition control module.
NOTE: Contaminated fuel or combustion air can create 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.
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