SERVICING
48
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2
PRIMARY LIMIT
CONTROL
The following drawing illustrates the style of limit switches
used on the 90% furnaces.
ENCLOSED DISK
FRONT VIEW SIDE VIEW
E
CEC
ER ERE ERC R
C EECRC R.
E ER
RCE E REE.
RE CE
RER E ER JR R E.
1. Remove burner compartment door to gain access to
the primary limit.
2. Remove low voltage wires at limit control terminals.
3. With an ohmmeter, test between these two terminals
as shown in the following drawing. The ohmmeter
should read continuous unless heat exchanger tem-
perature is above limit control setting. If not as above,
replace the control.
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,
temperature setting and color(s) code.
The auxiliary limit control is designed to prevent furnace
operation in case of main blower failure in horizontal or
The auxiliary limit control is suitable for both horizontal
direction, 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
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