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Safety Circuits
A number of safety circuits are employed to ensure safe and proper furnace operation. These circuits serve to control
any potential safety hazards and, as inputs in the monitoring and diagnosis of abnormal function. These circuits are
continuously monitored by the integrated control module.
Self Diagnostic Electronic Control Module
Certain furnace models are equipped with a self-diag-
nostic electronic control module. If a furnace component
is not operating properly, the control module will repeat-
edly flash a red light on and off in a factory-programmed
sequence, depending on the problem encountered.
If a furnace equipped with a self-diagnostic module is not
operating properly, look through the observation window
in the blower access door and make note of the number
of flashes in the sequence. Contact a qualified servicer
for further information. Do not attempt to troubleshoot the
problem yourself.
Auxiliary Limit
The auxiliary limit control is located on the blower deck
and monitors heat exchanger compartment tempera-
tures. It is a normally-closed (electrically), manual-reset,
temperature-activated sensor. This limit guards against
overheating as a result of insufficient conditioned air
passing over the heat exchanger. Disconnect electrical
power prior to removing the non-louvered door to reach
the secondary limit control. The control is in addition to
the main limit control and shuts the furnace off in case of
a blower failure. This control is a manual reset control,
which can be reset only once. If the unit goes off on limit
a second time, contact a qualified servicer so the problem
causing the control to open can be corrected.
Roll-out Limit Switches
The roll-out limit switches are normally-closed (electri-
cally), manual-reset, temperature-activated sensors. The
switches are mounted on the burner/manifold assembly
and monitors the burner flame. If there is an improper
draw of burner flames into the heat exchanger, the roll-
out limit switches will detect it and shutdown the gas
flowing to the burners,
WARNING
To avoid death, personal injury, or property damage,
due to fire or explosion, do not reset the roll-out
protection device. If it opens, the cause must be
investigated by a qualified servicer before any
attempt is made to engage the roll-out protection
device and turn the furnace back on.
Upflow
Auxiliary
Limit
Figure 3
Upflow Auxiliary Limit Location
