26
IO-247A
12/04
XIII. OPERATIONAL CHECKS
WARNING
T
O AVOID PERSONAL INJURY OR DEATH, DO NOT REMOVE ANY INTERNAL
COMPARTMENT COVERS OR ATTEMPT ANY ADJUSTMENT.
E
LECTRICAL
COMPONENTS ARE CONTAINED IN BOTH COMPARTMENTS.
T
O PREVENT
PROPERTY DAMAGE, PERSONAL INJURY OR DEATH DUE TO EXPLOSION
AND/OR FIRE, CONTACT A QUALIFIED SERVICE AGENT AT ONCE IF AN
ABNORMAL FLAME APPEARS.
B
URNER
F
LAME
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.
Check the burner flames for:
1. Good adjustment
2. Stable, soft and blue
3. Not curling, floating, or lifting off.
Burner Flame
A
UXILIARY
L
IMIT
C
ONTROL
A uto reset limits are located on or near the blower. To access this
auxiliary limit, disconnect the electrical power and remove the blower
door. If the limit control opens, the air circulation blower will run
continuously. The diagnostic light will flash one time. The auxiliary
limit control is designed to prevent furnace operation in case of
main blower failure on horizontal and counterflow installations. It
may also open if the power supply is interrupted while the furnace
is firing. The auxiliary limit control is suitable for both horizontal
right and horizontal left installations. Regardless of airflow direction,
it does not need to be relocated.
P
RIMARY
L
IMIT
The primary limit control guards against overheating resulting from
insufficient conditioned air passing over the heat exchanger. If the
primary limit control does not function during this test, the cause
must be determined and corrected. Function of this control should
be verified by gradually blocking the furnace return air after the
furnace has been operating (burners firing) for approximately ten
minutes. Check the control as follows:
1. Allow the furnace to operate with burners firing continuously
for approximately ten minutes.
2. Gradually block the return air to furnace. Remove airflow
blockage when limit control is activated and turns off burners.
Airflow blockage causes unit overheating and will produce
the following reactions:
• The gas valve to close and extinguish flame,
• The induced draft blower to be de-energized after a fifteen
second postpurge, and
• The circulator blower to remain energized continuously until
limit control resets.
3. Remove the return air blockage to clear overheating
condition. After an acceptable temperature is reached
during the cool down period, the limit control will reset and
allow the furnace to resume normal operation.
WARNING
T
O PREVENT PREMATURE FAILURE OF HEAT EXCHANGER, PROPERTY DAMAGE,
PERSONAL INJURY OR DEATH, DO NOT ADJUST THE LIMIT CONTROL (FACTORY
SET).
XIII. SAFETY CIRCUIT DESCRIPTION
IMPORTANT NOTE: This unit must not be used as a construction
heater during the finishing phases of construction of a new structure.
This type of use may result in premature failure due to extremely
low return air temperatures and exposure to corrosive or very dirty
atmospheres.
These checks establish that the primoary limit control is functioning
and will respond to a restriction in the return air, or a circulator
blower failure. If the primary limit control does not function during
this test, the cause must be determined and corrected.
G
ENERAL
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
NTEGRATED
C
ONTROL
M
ODULE
The integrated control module is an electronic device which controls
all furnace operations. Responding to the thermostat, the module
initiates and controls normal furnace operation, and monitors and
addresses all safety circuits. If a potential safety concern is
detected, the module will take the necessary precautions and
provide diagnostic information through an LED.
P
RIMARY
L
IMIT
The primary limit control is located on the partition panel and
monitors heat exchanger compartment temperatures. It is an
automatic reset, temperature sensor. The limit guards against the
overheating as a resulting of insufficient air passing over the heat
exchanger.
A
UXILIARY
L
IMIT
The auxiliary limit control is located either on or near the circulator
blower and monitors heat exchanger compartment temperatures.
The control is a temperature sensor. It guards against overheating
resulting from insufficient air passing over the heat exchanger.
R
OLLOUT
L
IMITS
The rollout limit controls are mounted on the burner/manifold
assembly and monitor the burner flame. They are manual-reset,
temperature sensors. This limit guards against burner flames not
being properly drawn into the heat exchanger.
P
RESSURE
S
WITCHES
The pressure switches are normally-open, 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. These switches guard against
insufficient airflow (combustion air and flue products) through the
heat exchanger.
F
LAME
S
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.
