Chevrolet 1980 Light Duty Truck Service Manual page 64

W ith ign. sw itch in " R u n " position
and heater or A /C on, locate short in
one of the fo llo w in g wires: (see note)
1. From fuse panel to master
switch on control.
2. From master switch to compressor
clutch.
3. M aster switch to blow er switch.
4. From blow er speed switch to
resistor.
5. From resistor to blo w er m otor.
N O T E : S hort c irc u it m ay be in te r­
m itte n t. If tester does not indicate
a short circuit, m ove heater harness
around as much as possible to re­
create short c ircuit. W atch and listen
fo r arcing.
Check FEED w ire from
resistor to blow er
speed sw itch.
I |
l a m p o n
o
Replace blow er
speed sw itch.
ELECTRICAL SYSTEM DI AGNOSTIC CHART
BLOWER MOTOR IN O PER ATIVE
(A N Y SPEED)
Check fo r proper
fuse
I
f u s e o k
The fo llo w in g tests should be made
w ith the ig n itio n sw itch in " R u n "
position, heater or A /C on and
blower sw itch on high.
Check blow er m o to r ground
T
( OR NO !
p o o r g r o u n d
|~Repair groun d] Check m o to r connector w ith
12 v o lt test light.
| LAM P L IG H T S ] |L A M P DOES NOT L IG H T ]
Check w ire connector on
Replace m otor
blow er relay w ith 12 v o lt test lig ht.
|LAM P L I G H T s j | LAMP D O E
Repair open in
Check w ire connector on blow er
wire from blower
relay w ith 12 vo lt test lig ht.
m otor to blow er
relay.
| LAM P DOES NOT U G H |
t
Use 12 vo lt test lig ht and check
w ire term inals at resistor.
L
LAM P OFF
JL
LAM P OFF
Repair open in wire
fro m blow er speed switch.
]
Disconnect resistor connectors, connect one iead
of a self powered test lig h t to any one term inal
and use the other lead to probe each o f the
other term inals.
_L
TEST LIG H T DOES NOT
GRO UND OK
L IG H T ON A L L T E R M IN A LS
-
I "
Replace resistor
I
[L A M P LIG H TS IN A L L P 0 S IT I0 N S |
" OT L IG H |
s n t Connect 12 v o lt test lig h t at wire
term inal on blow er relay (w ire
fro m resistor to blow er relay).
E LAM P L IG H T S I LAM P DOES NOT L IG H T !
E
I ^ A M P U O iH T S j Replace blow er relay. Repair Open in wire
fro m resistor to
Replace relay
blow er relay.
LAM P LIG H TS
Replace resistor
B LO W E R M O T O R IN O P E R A T IV E
(C E R T A IN S P E E D S -E X C E P T H IG H
ON C-K F O U R -S E A S O N )
TEST L IG H T LIG H TS ON
A L L T E R M IN A L S
X
W ith ignition switch in " R u n " position and heater
or A /C on, use 12 v o lt test lamp to check for
voltage at resistor connector w ith blo w er speed
switch in each position.
T
| LAM P DOES NO T L IG H T IN A L L P O S IT IO N S !
T u rn ignition key o ff and put H eater or A /C
C ontrol in o ff position. W ith blow er resistor w ire
connector disconnected, connect a ju m p e r lead
from battery positive term inal to the w ire term inal
in connector. Use 12 v o lt test light to j;h e c k fo r
voltage at w ire at blow er speed s w itc fic o n n e c to r.
Repeat same test on the other wires.
I
L A M P L IG H T S ON L A M P D O E S N O T L IG H T
A L L W IR E S ON A L L W IR E S
Repair open in
Replace blow er speed
switch. affected wire.