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F
O
M
AN
NLY
ODE
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.
•
96% models 115 VAC EAC 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.
•
EAC terminal is de-energized.
•
Furnace awaits next call from thermostat.
O
C
PERATIONAL
HECKS
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.
S
C
D
AFETY
IRCUIT
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 continuously monitored
during furnace operation by the integrated control module.
I
C
M
NTEGRATED
ONTROL
ODULE
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.
P
L
RIMARY
IMIT
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.
A
L
UXILIARY
IMIT
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.
R
L
OLLOUT
IMIT
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.
P
S
RESSURE
WITCHES
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.
F
S
LAME
ENSOR
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.
T
ROUBLESHOOTING
E
D
LECTROSTATIC
ISCHARGE
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
(ESD) P
RECAUTIONS
38
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