SERVICING
36
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 dimension, 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!
Disconnect 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. 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 induced
draft motor, reinstall burner compartment door.
7. Turn on electrical power and verify proper unit operation.
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,
pressure regulation, and 100 percent safety shut-off.
Two stage gas valves always require 24 volts between
common and low fire (main coil) to open.
Low (Main)
Common
High
White-Rodgers 2-Stage Valve
WARNING
Disconnect ALL power before servicing
CHECKING MAIN BURNERS
The main burners are used to provide complete
combustion 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.
Burners
Burners have been redesigned for 34.5” chassis furnaces.
Overall length and width dimensions remain the same as
40” model burners. The burners used 34.5” models have
burner head insert with larger diameter center hole and a
larger number of surrounding holes.
New 34.5 Burners
WARNING
Disconnect ALL gas and electrical power supply.
In checking main burners, look for signs of rust, oversized
and undersized carry over ports restricted with foreign
material, etc., burner cross-over slots should not be altered
in size.
