GMC 1986 P-Truck Service Manual page 81

1B-18 AIR CONDITIONING
| FUSE B L O W N ""]
WITH IGNITION SWITCH IN " RUN" POSITION AND
HEATER OR A/C ON, LOCATE SHORT IN ONE OF THE
FOLLOWING WIRES: (SEE NOTE)
1 FROM FUSE PANEL TO MASTER SWITCH ON
CONTROL.
2. FROM MASTER SWITCH TO COMPRESSOR
CLUTCH.
3. MASTER SWITCH TO BLOWER SWITCH.
4 FROM BLOWER SPEED SWITCH TO RESISTOR
5. FROM RESISTOR TO BLOWER MOTOR.
NOTE: SHORT CIRCUIT MAY BE INTERMITTENT. IF
TESTER DOES NOT INDICATE A SHORT CIRCUIT,
MOVE HEATER HARNESS AROUND AS MUCH AS
POSSIBLE TO RECREATE SHORT CIRCUIT WATCH
AND LISTEN FOR ARCING.
REPLACE BLOWER
SPEED SWITCH.
ELECTRICAL SYSTEM DIAGNOSTIC CHART
BLOW MOTOR INOPERATIVE
£
LAMP OFF
CHECK FEED WIRE FROM
RESISTOR TO BLOWER
SPEED SWITCH.
JL
LAMP ON | LAMP OFF
,,.J____1
REPLACE OPEN IN WIRE
FROM BLOWER SPEED
SWITCH.
Figure 18—Electrical System Diagnostic Chart
(ANY SPEED)
CHECK FOR PROPER
FUSE.
JL
|
THE FOLLOWING TESTS SHOULD BE MADE WITH
THE IGNITION SWITCH IN " RUN" POSITION,
HEATER OR A/C ON AND BLOW SWITCH ON
HIGH.
CHECK BLOWER MOTOR GROUND.
[
| POOR OR NO GROUND |
| REPAIR GROUND|
LAMP ON |
CHECK WIRE CONNECTOR ON BLOWER
| REPLACE MOTOR
RELAY WITH 12 VOLT TEST LIGHT.
1
LAMP ON
|
CHECK WIRE CONNECTOR ON
REPAIR OPEN IN WIRE
BLOWER RELAY WITH 12 VOLT
FROM BLOWER MOTOR
TO BLOWER RELAY.
TEST LIGHT.
LAMP DOES NOT LIGHT
USE 12 VOLT TEST LIGHT AND
CHECK WIRE TERMINALS AT
RESISTOR.
I
|
FUSE OK
Z
| GROUND OK 1
CHECK MOTOR CONNECTOR
WITH 12 VOLT TEST LIGHT
T
LAMP DOES NOT LIGHT
I
....
1
| LAMP DOES NOT LIGHT |
LAMP ON
] [
REPLACE RELAY.
1
LAMP ON
REPLACE RESISTOR.
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