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Cooling Mode
The normal operational sequence in cooling mode is as
follows:
•
R,Y, G thermostat contacts close, initiating a call for
cool.
• Integrated control module performs safety circuit
checks.
•
Outdoor fan and compressor are energized.
•
Circulator blower is energized on the cool speed.
•
Furnace circulator blower and outdoor cooling unit run
their appropriate speeds, integrated control module
monitors safety circuits continuously.
•
R,Y, G thermostat contacts open, completing the call
for cool.
•
Outdoor fan and compressor are de-energized.
•
Circulator blower continues running during a cool off
delay period of 45 seconds.
•
Furnace awaits next call from thermostat.
Fan Only Mode
The normal operational sequence in fan only mode is as
follows:
•
R and G thermostat contacts close, initiating a call for
fan.
• Integrated control module performs safety circuit
checks.
•
Circulator blower is energized on heat speed.
•
Circulator blower runs, integrated control module
monitors safety circuits continuously.
•
R and G thermostat contacts open, completing the
call for fan.
•
Circulator blower is de-energized.
•
Furnace awaits next call from thermostat.
OPERATIONAL CHECKS
The burner flames should be inspected with the burner
compartment door installed. Flames should be stable, quiet,
soft, and blue (dust may cause orange tips but they must not
be yellow). Flames should extend directly outward from the
burners without curling, floating, or lifting off. Flames must
not impinge on the sides of the heat exchanger firing tubes.
SAFETY CIRCUIT DESCRIPTION
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 control module.
INTEGRATED CONTROL MODULE
The integrated control module is an electronic device
which, if a potential safety concern is detected, 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, temperature-
activated sensor. The limit guards against overheating as a
result 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 blower compartment temperatures.
They are a normally-closed (electrically), manual-reset
sensors. These limits guard against overheating as a
result of insufficient conditioned air passing over the heat
exchanger.
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 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) negative air pressure-activated switches. They
monitor the airflow (combustion 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 insufficient airflow (combustion
air and flue products) through the heat exchanger and/or
blocked condensate drain conditions.
Flame Sensor
The flame sensor is a probe mounted to the burner/manifold
assembly which uses the principle of flame rectification to
determine the presence or absence of flame.
TROUBLESHOOTING
Electrostatic Discharge (ESD) Precautions
NOTE:
Discharge body’s static electricity before touching
unit. An electrostatic discharge can adversely affect electrical
components.
Use the following precautions during furnace installation
and servicing to protect the integrated control module from
damage. By putting the furnace, the control, and the person
at the same electrostatic potential, these steps will help
avoid exposing the integrated control module to electrostatic
discharge. This procedure is applicable to both installed and
uninstalled (ungrounded) furnaces.
1. Disconnect all power to the furnace. Do not touch
the integrated control module or any wire connected
to the control prior to discharging your body’s
electrostatic charge to ground.
2. Firmly touch a clean, unpainted, metal surface of the
furnace away from the control. Any tools held in a
person’s hand during grounding will be discharged.
