Chevrolet 1977 light duty truck Service Manual page 68

BLOWER M OTOR IN O P E R A T IV E
A T HIG H SPEED O N LY
(C-K FOUR-SEASON SYSTEM)
in-line fuse
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 short. Repair
short c irc u it as required.*
| C LIC K H E A R D I
— I -*
1
Check w ire term inal on relay
th a t goes to ju n ctio n block
w ith 12 v o lt test lamp.
LAM P L IG H TS I LAM P DOES NOT L IG H T ! I LAM P L IG H TS I
Repair open in w ire
fro m ju n c tio n block Check ground
Replace blow er
relay. to relay. on relay
r . . ... "
I
|G R O U N D o k | b a d g r o u n d
Replace relay Repair ground
* 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 circ u it,
move harness around as much 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 perform ing
the fo llo w in g checks.
E L E C T R IC A L S Y S T E M D IA G N O S T IC CHART
Check
I
W ith ig n itio n switch 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.
W ith ig n itio n sw itch in the
C-K M O D E L SYSTEMS
" R u n " positio n and the
1. Wire fro m fuse panel to master switch (on control).
heater or A /C on, move the
2. Master sw itch.
blow er speed sw itch to Hi.
3 .
Wire fro m master sw itch to therm ostatic switch.
Relay "c lic k " should be
4. Therm ostatic sw itch.
heard when sw itch is moved.
5. Wire fro m therm ostatic switch to discharge pressure switch.
6. Discharge pressure switch.
NO C LIC K H E A R D !
7. Wire fro m discharge pressure switch to compressor clutch
solenoid.
G M O D E L SYSTEMS
Check relay coil connector
1. Wire fro m fuse panel to a m plifier.
w ith 12 v o lt test lig h t.
2. A m p lifie r.
3.
Wires fro m a m p lifie r to therm ister.
4. Therm ister.
5. Wire fro m a m p lifie r to discharge pressure switch.
I LAM P DOES NOT L IG H T !
6. Discharge pressure sw itch.
7. Wire fro m discharge pressure switch to compressor clutch
Check w ire term inal on blower solenoid.
MOTOR HOME U N IT
speed switch connector w ith
1. Wire fro m fuse panel to blow er switch.
12 v o lt test light.
2. Blower switch.
3 .
Wire fro m blow er switch to therm ostatic switch.
4. Therm ostatic switch.
5. Wire fro m therm ostatic switch to compressor clu tch solenoid.
| | l a m p l i g h t s ) LAM P DOES
NOT L IG H T
I
1 1
Repair open Replace
in w ire fro m Blower speed
blow er speed switch.
switch to relay.
COMPRESSOR CLUTCH IN O P E R A T IV E *
^^hed^use^
| FUSE BLOWN |
| POOR OR NO G R 0 U N D |
Repair ground
I NO C L IC K H E A R D !
Replace solenoid
W ith ig n itio n sw itch in " R u n " p ositio n and A /C " 0 n " , check
fo r defective sw itch at the fo llo w in g locations. Using an external
jum per w ire, disconnect the electrical lead at the switch 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 witch.
2. Therm ostatic S w itch.
3. Discharge Pressure Switch.
G M O D E L SYSTEM
1. A m p lifie r.
2. Therm ister.
3. Discharge pressure sw itch.
MO TO R HOME U N IT
1. B lower sw itch.
2. Therm ostatic sw itch.
NO TE: If the compressor is s till inoperative a fte r the above
checks, check fo r power feed at each com ponent since
tw o or m ore com ponents are defective or there is an
open in the wires connecting the components.
FUSE OK |
Check Compressor S olenoid Ground
| GROUND O I
k
Disconnect connector on
compressor clu tch solenoid
and apply 12 volts to solenoid.
CLICK H E A R D