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A number of safety circuits are employed to ensure safe and proper furnace operation. These circuits serve to control
any potential safety hazards and serve as inputs in the monitoring and diagnosis of abnormal function. These circuits
are continuously monitored during furnace operation by the integrated ignition control.
Integrated Ignition Control
The integrated ignition control is an electronic device
which controls all furnace operations. Responding to the
thermostat, the module initiates and controls normal fur-
nace operation, and monitors and addresses all safety
circuits. If a potential safety concern is detected, the
module will take the necessary precautions and provide
diagnostic information through an LED.
Primary Limit
The primary limit control is located on the partition panel
and monitors heat exchanger compartment temperatures.
It is a normally-closed (electrically), automatic reset, tem-
perature-activated sensor. The limit guards against the
overheating as a resulting of insufficient conditioned air
passing over the heat exchanger.
Auxiliary Limit
The auxiliary limit controls are located on or near the
circulator blower and monitors heat exchanger compart-
ment temperatures. They are a normally-closed (electri-
cally), manual-reset, temperature activated sensor. These
limits guard against overheating as a result of insufficient
conditioned air passing over the heat exchanger.
Safety Circuit Description
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Rollout Limit
The rollout limit controls are mounted on the burner/
manifold assembly and monitor the burner flame. They are
normally-closed (electrically), manual-reset, temperature-
activated sensors. These limits guard against burner
flames not being properly drawn into the heat exchanger.
Pressure Switches
The pressure switches are normally-open (closed during
operation), single-pole single-throw, negative air pres-
sure-activated switches. They monitor the airflow (com-
bustion air and flue products) through the heat exchanger
via pressure taps located on the induced draft blower and
the coil front cover. These switches guard against insuffi-
cient airflow (combustion air and flue products) through the
heat exchanger and/or blocked condensate drain condi-
tions.
Flame Sensor
The flame sensor is a probe mounted to the burner/
manifold assembly which uses the principle of flame recti-
fication to determine the presence or absence of flame.
Burner Box
This furnace must use indoor air for combustion. It is not a
direct vent furnace, and it cannot be installed as a direct
vent furnace. The burner box is present only to reduce the
burner sound transmission.
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