Unit installation

10
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.
Upflow
Auxiliary
Limit
Figure 6
Upflow Auxiliary Limit Location
Manual Reset
Auxiliary Limit
Figure 7
Counterflow Auxiliary Limit Location
Auxiliary Limit
The auxiliary limit control is located on the blower deck
and monitors heat exchanger compartment temperatures
(Figures 6 and 7). It is a normally-closed (electrically),
manual-reset, temperature-activated sensor. This limit
guards against overheating as a result of insufficient con-
ditioned 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 ad-
dition 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.