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If the furnace is operating in the low-stage heating mode
when thermostat contacts open, circulator blower remains at
low-heat speed for the selected delay off period.
If the furnace is operating in high-stage heating mode when
the thermostat contacts open, the circulator blower remains
at high-heat speed for the selected heat-off delay period. The
circulator blower then switches to low-heat speed for the
remainder of the selected heat-off delay period. For example,
the selected heat-off delay period is 150 seconds. The
circulator blower operates at high heat for 30 seconds and at
low speed for 150 - 30 = 120 seconds.
■
Furnace awaits the next call from thermostat.
Cooling Mode
The normal operational sequence in cooling mode is as follows:
■
R and Y 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 cool speed following a fixed
5-second on delay. Electronic air cleaner terminals are
energized with circulator blower.
■
Furnace circulator blower and outdoor cooling unit run;
integrated control module monitors safety circuits
continuously.
■
R and Y thermostat contacts open, completing the call for
cool.
■
Outdoor fan and compressor are de-energized.
■
Circulator blower is de-energized following a fixed 45-second
cool off delay period. Electronic air cleaner terminals are
de-energized.
■
Furnace awaits the 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 low-heat speed. Electronic
air cleaner terminals are energized.
■
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. Electronic air cleaner
terminals are de-energized.
■
Furnace awaits the next call from thermostat.
Operational Checks
Burner Flame
The burner flames should be inspected with the burner
compartment door installed. A sight glass is provided for
inspection purposes. Flames should be stable, quiet, soft and
blue (dust may cause orange tips but must not be yellow). The
flames should extend directly outward from the burner without
curling, floating or lifting off. Flames must not impinge on the
sides of the heat exchanger firing tubes.
Burner Flame
Check the burner flames for good adjustment, a stable, soft and
blue flame that is not curling, floating or lifting off.
SAFETY CIRCUIT DESCRIPTION
General
A number of circuits are employed to ensure 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 Control
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 Control(s)
The auxiliary limit control(s) are located on or near the circulator
blower and monitors blower compartment temperatures. They
are 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 Control(s)
The rollout limit control(s) 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 on the burner/manifold
assembly which uses the principle of flame rectification to
determine the presence or absence of flame.
