Heater Circuit Diagnosis - GMC G Service Manual

1A-6 HEATING

HEATER CIRCUIT DIAGNOSIS

I-
FUSE BLOWN
' ...... . ' i
WITH THE IGNITION SW ITCH IN THE
"RUN" POSITION AND THE BLOW ER
o D c c n c iA /ir r 'u un M " i ic c
LOCATE A SH O RT IN ONE OF THE
FOLLOWING W IRES:
C D rtM T U C Cl ICC DAM CI T O T U C
1.
B L O W E R S P E E D S W IT C H .
2. FROM THE BLOW ER SPEED SWITCH
T O T H E H E A T E R H E S IS IU H .
3. FROM THE HEATER R ESISTO R TO
THE BLOWER.
M rv rc - o u n o T r i n n
a im t u c
B E IN T E R M IT T E N T . I F 1 H E M E 1 E H D U E S
NOT INDICATE A SH O RT CIRCUIT, MOVE
T H E H A R N E S S A H U U N U A S M U U H A S
POSSIBLE TO RE-CREATE A SH ORT
CIRCUIT. W ATCH AND LISTEN FOR
ARCING.
LAMP DOES NOT LIGHT
REPAIR THE OPEN IN THE BROW N W IR E FROM THE
Dl PrtA/CQ C D C C n CXA/ITOU T D T U P Cl ICC P A N C I
DISCONNECT THE RESISTO R CONNECTOR, CONNECT ONE LEAD OF A SELF POW ERED T E S T LIG HT TO
A N Y ONE TER M IN A L AND USE THE OTHER LEAD TO PROBE EACH OF THE OTHER TW O TERMINALS.
1
TEST LIGHT DOES NOT LIGHT
UN 1 n t 1
A LL tnlvlirM MLO.
~ T ........
REPLACE THE RESISTOR.
LAMP LIGHTS ON ALL TH REE W IR ES
REPLACE THE BLOW ER SPEED SWITCH.
ALL SPEEDS
CHECK THE FUSE IN THE FUSE PANEL.
TEST W ITH THE IGNITION SWITCH IN "R U N " POSITION, THE
BLOW ER SPEED SWITCH "O N " AND THE LEVER IN THE HEAT POSITION.
a m c t c q t o
POOR OR NO GROUND
REPAIR THE GROUND
i i t m a v
LAMP LIGHTS
REPLACE THE MOTOR
LAMP DOES NOT LIGHT
USE A 12-VOLT TEST LIGHT AND CHECK
THE FEED TERM IN AL (BROWN) ON THE
BLOW ER SPEED SWITCH.
1
i
W ITH THE IGNITION "O FF", DISCONNECT THE 3 W IR E C O N NEC TO R FROM
RESISTOR. CONNECT A JUM PER LEAD FROM TH E BA TTERY PO SITIVE
TERM IN AL TO AN Y W IR E TERM IN AL IN CONNECTOR. USE A 12-VOLT T EST
LIGHT TO CHECK FOR VOLTAG E AT THE C O RRESPO N DING W IR E ON THE
BLOW ER SPEED SWITCH. R EPEAT THE SAME TEST ON THE O THER WIRES.
Figure 4 — Heater Circuit Diagnosis
BLOW ER M OTOR INOPERATIVE
|
CERTAIN SPEED S ONLY
FUSE OK
CHECK THE BLOW ER MOTOR GROUND.
CHECK THE M O TO R CONNECTOR
IA/ITU A n
CHECK THE BLOW ER FEED W IR E
UN i n c
R ESISTO R WITH A 12-VOLT TEST LIGHT.
I
1
LAMP LIGHTS
REPLACE THE SWITCH
I
I
1
TEST LIGHT LIGHTS ON ALL THE TERM IN ALS
1
I A M P I IR H T S D N Al 1 T H R F F W IR F S
LAMP DOES NOT LIGHT ON ALL TH REE W IR ES
REPAIR THE OPEN IN AFFECTED WIRE.
I
1
GROUND OK
T T C C T 1 1/1U T
\ i n > l
LAMP DOES NOT LIGHT
i u n m e
o u i n i n c o u in
LAMP LIGHTS
REPAIR THE OPEN IN
THE FEED W IR E FROM
THE R ESISTO R TO THE
tJ L U W E H M U I U H .
1
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L00176