SERVICING
52
S-300 TESTING PRIMARY LIMIT CONTROL
APG/GPG units use a snap-disk type primary limit device.
Sometimes referred to as "stat on a stick". The limit setting
is fixed and must not be readjusted in the field.
Volt / Ohm
Meter
COLOR
IDENTIFYING
SLEEVES
TESTING PRIMARY LIMIT CONTROL
Refer to the specification section to determine the proper limit
cutout temperature for the model being serviced.
In all instances the limit control is wired in series with the
ignition control.
If the temperature within the furnace should exceed this
setting, the control will open, de-energizing the ignition
control which in turn will open the electrical circuit to the gas
valve.
The control will automatically reset when the temperature
within the combustion chamber is sufficiently lowered.
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 electrical power to unit. Some units may have
more than one source of power.
2. Remove the wires from the limit control terminals.
3. Using an ohmmeter, test for continuity across the two
terminals.
4. If limit test open allow unit to cool and retest.
5. If still open, replace the control.
S-301 TESTING AUXILIARY LIMIT
The auxiliary limit control is a preset nonadjustable control
mounted in the blower compartment area.
It is connected in series with the rollout switch wiring to the
gas valve. If its temperature should be exceeded, it will open,
interrupting the voltage to the gas valve causing it to open.
An additional limit (primary limit) control is required for safety
control of high temperature within the furnace or ductwork.
AUX. LIMIT
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 the wires from the auxiliary limit control termi-
nals.
2. Using an ohmmeter, test for continuity across the two
terminals. No reading indicates the control is open. Push
the red reset button, test again - if still open, replace the
control.
