SERVICING
49
Manual or Automatic Reset Auxiliary Limits Located in
Blower Side
WARNING
HIGH
VOLTAG
E
D
IS
C
ONN
EC
T
ALL
POW
ER
B
E
FO
RE
S
ER
VI
C
ING
O
R
INSTALLING
THIS
UNIT
.
M
ULTIPL
E
POW
ER
SOU
RCE
S
MAY
B
E
P
RE
S
E
NT
.
F
AILU
RE
TO
DO
SO
MAY
C
AUS
E
P
R
OP
ER
TY
DAMAG
E
,
P
ER
SONAL
IN
J
U
R
Y
O
R
D
E
ATH
.
1. Remove the wires from the auxiliary limit control termi-
nals.
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
POSSIBL
E
FI
RE
,
ONLY
RE
S
E
T
TH
E
AU
X
ILIA
R
Y
LIMIT
C
ONT
R
OL
ON
CE.
I
F
IT
SHOULD
OP
E
N
A
S
EC
OND
TIM
E
,
A
Q
UALIFI
E
D
S
ER
VI
CER
MUST
D
E
T
ER
MIN
E
WHY
TH
E
AU
X
ILIA
R
Y
LIMIT
OP
E
N
E
D
B
E
FO
RE
RE
S
E
TTING
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.
*
*
*
*
*
*
*
2
FLAME
ROLLOUT
SWITCHES
Flame Rollout Switch Location
(90% Upflow Furnace Shown, Counterflow 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.
L
IN
E
VOLTAG
E
NOW
P
RE
S
E
NT
WARNING
1. Remove the burner compartment door to gain access to
the rollout switch(es) mounted to burner bracket.
2. Reset the manual rollout switch.
3. Remove wires from rollout switch.
4. Using an ohmmeter, check for continuity across the swtch.
5. if the switch will not close after manually resetting, it must
be replaced.
If a roll out switch has tripped, it is important to find out why.
Possible causes could be flame impingement, orifice plate out
of position, burners with excessive cross-over slot dimension,
over-firing, improper orifices, improper gas pressure, air
leaking from around the heat exchanger into the burner
compartment, air leaking through the heat exchanger itself.
6. After check and/or replacement of rollout switch, reinstall
burner compartment door and verify proper unit operation.
INDUCED DRAFT BLOWER MOTOR
WARNING
HIGH
VOLTAG
E
D
IS
C
ONN
EC
T
ALL
POW
ER
B
E
FO
RE
S
ER
VI
C
ING
O
R
INSTALLING
THIS
UNIT
.
M
ULTIPL
E
POW
ER
SOU
RCE
S
MAY
B
E
P
RE
S
E
NT
.
F
AILU
RE
TO
DO
SO
MAY
C
AUS
E
P
R
OP
ER
TY
DAMAG
E
,
P
ER
SONAL
IN
J
U
R
Y
O
R
D
E
ATH
.
1. Remove burner compartment door to gain access to
the induced draft blower motor.
2. Disconnect the motor wire leads from its connection
point at the induced draft motor.
