SERVICING
57
THERMODISC (TOD) 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 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 combustion chamber is sufficiently lowered.
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 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 CONTROL
This control is preset nonadjustable control mounted in the
blower compartment area.
It is connected in series with the limit control wiring to the
ignition control. If its temperature should be exceeded, it will
open, interrupting the voltage to the gas valve causing it to
open.
AUX. LIMIT
WARNING
D
ISCONNECT ELECTRICAL POWER SUPPLY.
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.
OHMMETER
LIMIT OR AUXILIARY LIMIT CONTROL
S-302 CHECKING FLAME ROLLOUT SWITCH
Package Gas Units with serial numbers beginning 9001 and
later use a temperature activated manual reset control
mounted to the manifold assembly.
This control is wired in series with the primary limit and inte-
grated control. 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.