SERVICING
115
VOLT / OHM
METER
Testing Primary Limit Control
(80% Furnaces)
VOLT / OHM
METER
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 opera-
tion.
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.
S-301 CHECKING AUXILIARY LIMIT CONTROL
The
80% single stage
furnaces use a auxiliary limit (auto-
matic reset) control connected in series with the gas valve
and integrated control module. If its temperature should be
exceeded, it will open, interrupting the voltage to the gas
valve causing it to close. The auxiliary limit is located on
the front side of the blower housing, near the center, on all
80% single-stage furnaces, as shown in the following illus-
tration.
BLOWER HOUSING
AUXILIARY LIMIT CONTROL
Auxiliary Limit Control Location
(All 80% Single-Stage Furnaces)
All
90% single-stage
upflow furnaces use one auxiliary limit
switch for control of high temperatures within the furnace or
duct work. This control is preset, nonadjustable and must
be manually reset. The control is located in the blower com-
partment of the furnace on the blower deck, as shown in the
following illustration.
AUXILIARY LIMIT
CONTROL
BLOWER DECK
Auxiliary Limit Control Location
(All 90% Single-Stage Furnaces)
All 80% and 90% two-stage furnaces and 90% single-stage
counterflow furnaces, use (2) two auxiliary limits located on
the blower housing (one on each side), as shown in the
following illustration.