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These checks establish that the primary 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.
WARNING
To prevent personal injury or death, do not remove any internal compartment covers or attempt any adjustment.
Electrical components are contained in both compartments. Contact a qualified service agent at once if an
abnormal flame appearance should develop.
WARNING
To prevent death, personal injury or property damage due to fire, follow these directions for the auxiliary limit
control. If the auxiliary limit control opens, it may be reset one time only.
WARNING
To prevent death, personal injury, property damage or premature failure of heat exchanger, do not adjust the
primary limit control (factory set).
Operational Checks
Auxiliary Limit
A manual 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 four times. These symptoms are identical to
a trip of the primary limit control.
The auxiliary limit control is designed to prevent furnace
operation in case of main blower failure on horizontal
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 di-
rection, it does not need to be relocated.
(
SERVICER’S NOTE:
If it becomes necessary to slide the
blower assembly out of the furnace, the auxiliary limit
control should be removed first. After the blower assembly
is reinstalled, the auxiliary limit must be reinstalled.)
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 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
