62
SERVICING
*
*
*
*
*
*
*
2
FLAME
ROLLOUT
SWITCHES
Flame Rollout Switch Location
(90% Upflow Furnace Shown, Counterflow Similar)
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 rollout control
opens, the air circulation blower will run continuously.
L
INE VOLTAGE NOW PRESENT
WARNING
1. Remove the burner compartment door to gain access to
the rollout switch(es) mounted to burner bracket.
2. Reset the manual rollout switch.
3. Remove wires from rollout switch.
4. Using an ohmmeter, check for coninuity across the switch.
5. If the switch will not close after manually resetting, it must
be replaced.
If a roll out switch has tripped, it is important to find out why.
Possible causes could be flame impingement, orifice plate
out of position, burners with excessive cross-over slot dimen
-
sion, over-firing, improper orifices, improper gas pressure,
air leaking from around the heat exchanger into the burner
compartment, air leaking through the heat exchanger itself.
6. After check and/or replacement of rollout switch, reinstall
burner compartment door and verify proper unit operation.
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 tri
-
al 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 induced
draft motor, reinstall burner compartment door.
7. Turn on electrical power and verify proper unit opera
-
tion.
CHECKING MODULATING GAS VALVE
The gas valve on ComfortBridge™ Modulating Furnace uses
a 24VAC electrically stepped valve by White Rodgers. The
furnace will fire at 100% firing rate for the first heating cycle.
Based on the furnace internal control algorithms the gas
valve and induced draft blower will modulate to provide the
correct gas input needed. The valve provides control of the
main burner gas flow, pressure regulation, and 100 percent
safety shut off.
NOTE:
Upon power up, the gas valve stepper motor may
activate to change position. This actually is a calibration pro
-
cess for the modulating gas valve. During this event a slight
clicking sound from the stepper motor may be heard. This
clicking sound is inherent to the stepper motor and does not
indicate a problem.
The front cover pressure switch is wired in series with Pin 5
on the gas valve (24 volt hot) so if you are not getting voltage
to the valve ensure the front cover pressure switch is closed.
Recommend voltage checks on the gas valve:
PIN 5 - TH - MAIN VALVE 24 VAC
PIN 4 - TR - GROUND
PIN 3 - TX - COMMUNICATION TO IFC 3.3 VDC
PIN 2 - RX - COMMUNICATION TO STEPPER 5.0 VDC
PIN 1 - TH - BOARD 24 VAC
