SERVICING
35
S-301 CHECKING AUXILIARY LIMIT CONTROL
BLOWER HOUSING
AUXILIARY LIMIT CONTROL
Auxiliary Limit Control Location
WARNING
HIGH
VOLTAGE
D
I
S
CONNECT
ALL
POWE
R
BEFO
R
E
S
E
R
VICING
O
R
IN
S
TALLING
THI
S
UNIT.
M
ULTIPLE
POWE
R S
OU
R
CE
S
MAY
BE
P
R
E
S
ENT.
F
AILU
R
E
TO
DO
S
O
MAY
CAU
S
E
P
R
OPE
R
TY
DAMAGE,
PE
RS
ONAL
IN
J
U
R
Y
O
R
DEATH.
RED
RESET
BUTTON
COLOR
IDENTIFYING
Testing Auxiliary Limit Control
WARNING
T
O
AVOID
PO
SS
IBLE
FI
R
E,
ONLY
R
E
S
ET
THE
AU
X
ILIA
R
Y
LIMIT
CONT
R
OL
ONCE.
I
F
IT
S
HOULD
OPEN
A
S
ECOND
TIME,
A
Q
UALIFIED
S
E
R
VICE
R
MU
S
T
DETE
R
MINE
WHY
THE
AU
X
ILIA
R
Y
LIMIT
OPENED
BEFO
R
E
R
E
S
ETTING
AGAIN.
S-302 CHECKING FLAME ROLLOUT CONTROL
A temperature activated manual reset control is mounted to
the manifold assembly on 80% furnaces,
ROLLOUT
SWITCH
Flame Rollout Switch Location
(80% Upflow Furnace Shown, Downflow Similar)
The control is designed to open should a flame roll out occur.
An over firing condition or flame impingement on the heat
shield may also cause the control to open. If the rollout control
opens, the air circulation blower will run continuously.
On single-stage 80% the ignition control diagnostic light will
flash (6) six times indicating a trip of the rollout switch. (on
some models this also indicates an open control board fuse)
L
INE
VOLTAGE
NOW
P
R
E
S
ENT
WARNING
1. Remove the burner compartment door to gain access to
the rollout switch(es) mounted to burner bracket.
The servicer should reset the ignition control by opening and
closing the thermostat circuit. Then look for the ignitor glowing
which indicates there is power to the ignition control. Measure
the voltage between each side of the rollout control and
ground while the ignition control tries to power the gas valve.
2. Measure the voltage between each side of the rollout
control and ground during the ignition attempt. Refer to
the following figure.
