Table of Contents
Advertisement
Circulator blower continues running during a cool-off delay
period. The Off delay time and airflow level are determined by
the selected ramping profile.
Electronic air cleaner terminal and circulator blower are
de-energized.
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 continuous fan speed (30%
of the furnace's maximum airflow capability) following a
5-second delay. Electronic air cleaner terminal is energized.
Circulator blower runs; Integrated control module monitors
safety circuits continuously.
R and G thermostat contacts open, completing the call for
fan.
Electronic air cleaner terminal and circulator blower are
de-energized.
Furnace awaits next call from thermostat.
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 Controls
The auxiliary limit controls 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.
28
SAFETY CIRCUIT DESCRIPTION
Operational Checks
Burner Flame
The burner flames should be inspected with the burner
compartment door installed. Flames should be stable, soft and
blue (dust may cause orange tips but must not be yellow). The
flames must 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.
Rollout Limit Controls
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 on the burner/manifold
assembly which uses the principle of flame rectification to
determine the presence or absence of flame.
Advertisement
Table of Contents
