52
SERVICING
The control is designed to open should a flame roll out
occur. An over firing condition or flame impingement on the
heat shield may also cause the control to open. If the roll-
out control opens, the air circulation blower will run con-
tinuously.
On single-stage 80% and 90% models, the ignition control
diagnostic light will flash (6) six times indicating a trip of
the rollout switch.
L
INE VOLTAGE NOW PRESENT
WARNING
1. Remove the burner compartment door to gain access
to the rollout switch(es) mounted to burner bracket.
The servicer should reset the ignition control by opening
and closing the thermostat circuit. Then look for the ignitor
glowing which indicates there is power to the ignition con-
trol. Measure the voltage between each side of the rollout
control and ground while the ignition control tries to power
the gas valve.
2. Measure the voltage between each side of the rollout
control and ground during the ignition attempt. Refer to
the following figure.
VOLT / OHM
METER
GN
D
RED
RESET
BUTTON
COLOR
IDENTIFYING
TAB
Checking Flame Rollout Switch
a. If no voltage is measured on either side of control it
indicates ignition control or wiring to control prob-
lem.
b. If voltage is measured on one side of the control and
not the other it indicates the control is open.
c. If voltage is measured on both sides of the control
the wiring to gas valve or valve is at fault.
3. After check and/or replacement of rollout switch, rein-
stall burner compartment door and verify proper unit op-
eration.
S-303 INDUCED DRAFT BLOWER Motor
WARNING
HIGH
VOLTAGE
D
ISCONNECT
ALL
POWER BEFORE SERVICING OR
INSTALLING THIS UNIT.
M
ULTIPLE POWER SOURCES MAY
BE PRESENT.
F
AILURE TO DO SO MAY CAUSE PROPERTY
DAMAGE, PERSONAL INJURY OR DEATH.
1.
Remove burner compartment door to gain access to
the induced draft blower motor.
2.
Disconnect the motor wire leads from its connection
point at the induced draft motor.
3.
Using a ohmmeter, test for continuity between each
of the motor leads.
4.
Touch one probe of the ohmmeter to the motor frame
(ground) and the other probe in turn to each lead.
If the windings do not test continuous or a reading is
obtained to ground, replace the motor.
5. If the windings have a continuity reading, reconnect
wires. Turn power on to the furnace and turn the
thermostat on in the heating mode. Check voltage
for 115V at the induced draft motor terminals during
the trial for ignition. If you have 115V and the motor
does not run, replace the induced draft motor.
6.
After completing check and/or replacement of in-
duced draft motor, reinstall burner compartment door.
7.
Turn on electrical power and verify proper unit opera-
tion.
S-304 CHECKING GAS VALVE (Redundant)
A combination redundant operator type gas valve which
provides all manual and automatic control functions required
for gas fired heating equipment is used.
The valve provides control of main burner gas flow, pres-
sure regulation, and 100 percent safety shut-off.
WARNING
D
ISCONNECT
ALL
POWER BEFORE SERVICING
Single stage gas valves should be tested on the furnance
with 24 VAC connected to the gas valve and manometers
reading supply line and manifold pressures.
S-305 CHECKING MAIN BURNERS
The main burners are used to provide complete combus-
tion of various fuels in a limited space, and transfer this
heat of the burning process to the heat exchanger.
Proper ignition, combustion, and extinction are primarily
due to burner design, orifice sizing, gas pressure, primary
and secondary air, vent and proper seating of burners.
