Chevrolet 1977 light duty truck Service Manual page 67

B L O W E R M O T O R I N O P E R A T I V E
( A N Y SPE E D )
Check for proper
fuse
| F U S E B L O W N !
With ign. switch in " R u n " position
and heater or A/C on, locate short in
one of the following wires: (see note)
C-K Four-Season System
1. From fuse panel to master
switch on control.
2. From master switch to compressor | P O O R O R NO G R 0 U N D |
clutch.
3. Master switch to blower switch.
| R e pai r g r o u n d ]
4. From blower speed switch to
resistor.
6. From resistor to blower motor.
| L A M P L I G H T s l
Except C-K Four-Season
Repl ac e m o t o r
1. From fuse panel to blower switch.
2. From blower switch to resistor.
3. From resistor to blower motor.
I L A M P L I G H T S
N O TE: Short circuit may be inter­
mittent. If tester does not indicate
Repai r open in
a short circuit, move heater harness
w i r e f r o m b lo w e r
around as much as possible to re­
m o t o r to b l o w e r
create short circuit. Watch and listen
relay.
for arcing.
| L A M P D O E S N O T L I G H T j
Use 12 v o l t tes t l i g h t a nd c hec k
w i r e t er m i n al s at r esis tor .
L A M P O F F
T
Che ck F E E D w i re f r o m
re si stor t o b l o w e r
speed s w i t c h .
| |
l a m p q n ' L A M P O F F I
_
I
R epl a ce b lo w e r
Re p ai r o pen in wi r e
speed s w i t c h .
f r o m b lo w e r speed s w i t c h .
ELECTRICAL SYSTEM DIAGNOSTIC CHART
( )
f u s e o k
T h e f o l l o w i n g tests sh ou ld be made
w i t h the i g n i ti o n s w i t c h in " R u n "
p o s i t i o n , heater or A / C on and
b l o w e r s w i t c h on high.
Chec k b l o w e r m o t o r g r o un d
X
X
I g R O U N D O k I
Chec k m o t o r c o n n e c t o r w i t h
12 v o l t tes t l i ght.
JL
L A M P D O E S N O T L I G H T l
Check w i r e c o n n e c t o r on
b l o w e r r elay w i t h 12 v o l t test l i gh t.
| L A M P D O E S N O T L I G H T )
Check w ir e c o n n e c t o r on b l o w e r
r elay w i t h 12 v o lt tes t l ight.
I !
l a m p l i g h t s
Repl ac e rel ay
X
L A M P L I G H T S
Repl ace resistor
B L O W E R M OTOR 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 IGH
ON C-K F O U R - SE A SO N )
Disconnect resistor connectors, connect one lead
of a self powered test light to any one terminal
and use the other lead to probe each of the
other terminals.
T E S T L I G H T DO E S NO T
L I G H T O N A L L T E R M I N A L S
I
Repl ace resistor
[ L A M P L I G H T S IN A L L P O S I T I O N S |
Co nne ct 12 v o lt test light at wi re
t e r m in a l on b lo w e r rel ay (wire
f r o m resistor t o b l o w e r relay).
1
I L A M P L I G H T S l | L A M P DOES N O T L I G H T |
X
X
Replace b lo w e r relay. Repai r open in wi re
f r o m resi stor to
b l o w e r relay.
Replace b l o w e r speed
switch.
T E S T L I G H T L I G H T S ON
A L L T E R M I N A L S
X
With ignition switch in " R u n " position and heater
or A/C on, use 12 volt test lamp to check for
voltage at resistor connector with blower speed
switch in each position.
X
1
L A M P D O E S N O T L I G H T I N A L L P O S I T I O N S
Turn ignition key off and put Heater or A/C
Control in off position. With blower resistor wire
connector disconnected, connect a jumper lead
from battery positive terminal to the wire terminal
in connector. Use 12 volt test light to check for
voltage at wire at blower speed switch connector.
Repeat same test on the other wires.
X
LA M P L IG H T S ON
L A M P D O ES NO T L IG H T
A L L W IR E S
ON A L L W IR E S
Repai r open in
a ff e c te d w ir e.