Goodman [A/G]PG, Service Instructions Manual

Page: 45 / 52

SERVICING
45
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
In all instances the limit control is wired in series with the
ignition control.
If the temperature within the appliance should exceed this set-
ting, 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 unit is sufficiently lowered.
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 ter-
minals.
4. If limit tests open, allow unit to cool and retest.
5. If still open, replace the control.
Limit Switch Operation (applies to Primary) Direct Spark
Ignition (DSI) systems.
If a limit switch opens, the indoor blower is energized on heat
speed and the induced draft blower is energized. The LED on
the control flashes "4" to indicate an open limit switch. The
blower and inducer remain on while the limit switch is open.
The gas valve is de-energized. Power to the thermostat "R" is
removed while the limit switch is open.
When the limit switch re-closes, the induced draft motor runs
through its post purge and the indoor blower goes through the
heat off delay.
If a call for heat exists when the limit switch re-closes, the
control goes through a pre-purge period and then makes an
ignition attempt. The indoor blower remains on (for the delay
off time) during the re-ignition attempt.
1. If no voltage is measured on either side of control it indi-
cates ignition control or wiring to control problem.
2. If voltage is measured on one side of the control and
not the other, it indicates the control is open.
3. If voltage is measured on both sides of the control the wir-
ing to the gas valve is at fault.
S-301 TESTING AUXILIARY LIMIT
The auxiliary limit control is an automatic reset, 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 unit or duct work.
AUX. LIMIT
1. Remove the wires from the auxiliary limit control terminals.
2. Using an ohmmeter, test for continuity across the two ter-
minals. No reading indicates the control is open. If limit
tests open, allow to cool and retest.
3. If still open, replace the control.