Instructions / Assembly

47
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 con-
ditioned 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 opera-
tion) 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 insuffi-
cient 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 de-
termine the presence or absence of flame.
Burner Flame
Figure 57
T ROUBLESHOOTING
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.
• Furnace is now operating on the specified stage
called for by the two-stage thermostat.
• Furnace runs, integrated control module monitors
safety circuits continuously.
• If the two-stage thermostat changes the call from
low heat to high heat, the integrated control module
will immediately switch the induced draft blower,
gas valve, and circulator blower to their high stage
settings.
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 (25, 50, 75 or 100% of the furnace’s maximum
airflow capability. Fan speed selected by dip
switches) following a five (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.
• Circulator blower is de-energized. Electronic air
cleaner terminal is de-energized.
• Furnace awaits next call from thermostat.
O PERATIONAL C HECKS
The burner flames should be inspected with the burner compart-
ment 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.
S AFETY C IRCUIT D ESCRIPTION
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 continu-
ously monitored during furnace operation by the integrated con-
trol module.
INTEGRATED CONTROL MODULE
The integrated control module is an electronic device which, if a
potential safety concern is detected, will take the necessary pre-
cautions 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-ac-
tivated sensor. The limit guards against overheating as a result
of insufficient conditioned air passing over the heat exchanger.