Chevrolet 1977 light duty truck, Service Manual

Page: 68 / 861

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Diagnosis
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E L E C T R IC A L S Y S T E M D IA G N O S T IC CHART
BLOW ER M OTOR IN O P E R A T IV E
A T HIG H SPEED O N L Y
(C-K FOUR-SEASON SYSTEM)
Check
in -line fuse
I
FUSE B L O W N !
Connect Tester. Use to check
w ire fro m ju n c tio n to blow er
relay to locate sh ort. Repair
sh ort c irc u it as re q uired .*
W ith ig n itio n sw itch in the
" R u n " p ositio n and the
heater or A /C on, move the
b lo w e r speed sw itch to Hi.
Relay " c lic k ” should be
heard when sw itch is moved.
| C L IC K H E A R D I
1
— I -*
NO C L IC K H E A R D !
Check w ire term in al on relay
th a t goes to ju n c tio n block
w ith 12 v o lt test lamp.
Check relay co il co nnector
w ith 12 v o lt test lig h t.
LAM P L IG H TS I LAM P DOES NOT L IG H T ! I LAM P L IG H T S I I LAM P DOES NOT L IG H T !
Replace blow er
relay.
Repair open in w ire
fro m ju n c tio n b lo ck
to relay.
Check ground
on relay
Check w ire term in al on blow er
speed sw itch co nn ecto r w ith
12 v o lt test lig h t.
r ..... “
|G R O U N D
o k
I
|
b a d g r o u n d
|
Replace relay Repair ground
|
l a m p l i g h t s
) LAM P DOES
NOT L IG H T
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1
1
Repair open Replace
in w ire fro m
B low er speed
blow er speed switch.
sw itch to relay.
* S h o rt c irc u it may be in te rm itte n t.
If tester does n o t indicate a short c irc u it,
move harness around as m uch as possible
to re-create short c irc u it. Watch and
listen fo r arcing.
* * R e fe r to W iring Diagrams w h ile perfo rm ing
the fo llo w in g checks.
COMPRESSOR CLUTCH IN O P E R A T IV E *
^^hed^use^
| FUSE BLOWN |
W ith ig n itio n sw itch in " R u n ” position, and A /C " O n " , connect
tester and locate short in one o f the fo llo w in g wires or com po­
nents. Replace a shorted w ire o r defective switch.
C-K M O D E L SYSTEMS
1. W ire fro m fuse panel to master switch (on co ntro l).
2. Master sw itch.
3.
Wire fro m master sw itch to therm ostatic switch.
4. Th erm o sta tic sw itch.
5. W ire fro m the rm osta tic sw itch to discharge pressure switch.
6. Discharge pressure sw itch.
7. W ire fro m discharge pressure switch to compressor clutch
solenoid.
G M O D E L SYSTEMS
1. Wire fro m fuse panel to a m p lifie r.
2. A m p lifie r.
3.
Wires fro m a m p lifie r to therm ister.
4. T h erm ister.
5. W ire fro m a m p lifie r to discharge pressure switch.
6. Discharge pressure sw itch.
7. W ire fro m discharge pressure switch to compressor clutch
solenoid.
MOTOR HOME U N IT
1. W ire fro m fuse panel to blow er switch.
2. B low er switch.
3.
W ire fro m b lo w e r sw itch to therm ostatic switch.
4. Th erm o sta tic sw itch.
5. Wire fro m the rm osta tic sw itch to compressor clu tch solenoid.
FUSE OK |
Check Compressor S olenoid Ground
| POOR OR NO G R 0 U N D |
Repair ground
| GROUND O
k
I
Disconnect co nnector on
compressor clu tch solenoid
and a pp ly 12 vo lts to solenoid.
I NO C L IC K H E A R D ! C LIC K H E A R D
Replace solenoid
W ith ig n itio n sw itch in " R u n ” p o sitio n and A /C ” 0 n ” , check
fo r defective sw itch at the fo llo w in g locations. Using an external
ju m p er w ire, disconnect the e lectrical lead at the sw itch and
ju m p the sw itch term inals (see "W irin g Diagrams” ).
C-K M O D E L SYSTEM
1. Master S w itch.
2. T h erm o sta tic S w itch .
3. Discharge Pressure Switch.
G M O D E L SYSTEM
1. A m p lifie r.
2. T h erm ister.
3. Discharge pressure sw itch .
MO TO R HOME U N IT
1. B lower sw itch.
2. T h erm o sta tic sw itch.
NO TE : If the compressor is s till inoperative a fte r the above
checks, check fo r power feed at each co m p on en t since
tw o or m ore com ponents are defective or there is an
open in the wires connecting the com ponents.
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