SERVICING
61
COLOR
IDENTIFYING
TAB
Testing Primary Limit Control
(90% Furnaces)
4. After completing check and/or replacement of primary
limit control, reinstall burner compartment door.
5. Turn on electrical power and verify proper unit operation.
To aid in identifying these controls, refer to the
Primary Limit
Charts
in furnace Technical Manual for part number, tempera
-
ture setting and color(s) code.
CHECKING AUXILIARY LIMIT CONTROL
The auxiliary limit control is designed to prevent furnace
operation in case of main blower failure in horizontal or coun
-
terflow 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 direc
-
tion, it does not need to be relocated. The (2) two auxiliary
limits are located on the blower housing (one on each side),
as shown in the following illustration.
LIMIT
AUXILIARY LIMIT
CONTROL
AUXILIARY LIMIT
CONTROL
BLOWER HOUSING
Auxiliary Limit Control Location
(Select 90% / 95% Furnaces)
MANUAL OR AUTOMATIC RESET AUXILIARY
LIMITS LOCATED IN BLOWER SIDE
WARNING
HIGH
VOLTAGE
D
ISCONNECT
ALL
POWER BEFORE SERVICING OR
INSTALLING THIS UNIT.
M
ULTIPLE POWER SOURCES MAY
BE PRESENT.
F
AILURE TO DO SO MAY CAUSE PROPERTY
DAMAGE, PERSONAL INJURY OR DEATH.
1. Remove the wires from the auxiliary limit control terminals.
2. Using an ohmmeter, test for continuity across the two
terminals (only test when the auxiliary limit is at room
temperature).
RED
RESET
BUTTON
COLOR
IDENTIFYING
Testing Auxiliary Limit Control
WARNING
T
O AVOID POSSIBLE FIRE, ONLY RESET THE AUXILIARY LIMIT CONTROL
ONCE.
I
F IT SHOULD OPEN A SECOND TIME, A QUALIFIED SERVICER
MUST DETERMINE WHY THE AUXILIARY LIMIT OPENED BEFORE
RESETTING AGAIN.
CHECKING FLAME ROLLOUT CONTROL
A temperature activated manual reset control is mounted to
the manifold assembly on 90% furnaces, as shown in the
following illustration.
