Chevrolet 1977 light duty truck, Service Manual

Page: 34 / 861

INSUFFICIENT HEAT DIAGNOSIS
P osition th e c o n tro ls so th a t the:
Te m p eratu re lever is o n fu ll heat.
S elector o r heater lever is o n Heater.
Fan sw itch is o n H i.
| *C H E C K D U M P D O O R O U T L E T FOR A IR FLO W ~ |
N O A IR FLO W
CHECK D E F R O S T E R O U T L E T S FO R A IR FLOW
( I f in d o u b t as to High o r L o w a ir flo w
set selector o n D E F w h ic h is H igh and
com pare.
Reset selector o n Heater)
A d ju s t d u m p d o o r fo r no a ir flo w .
NO OR LOW A IR FLOW
C H E C K H E A T E R O U T L E T A IR FLOW
( If in d o u b t, sw itch fan
sw itch fro m Hi to Lo)
H IG H A IR FLOW
J
A d ju s t d e fro ste r d o o r fo r lo w a ir flo w .
C H A N G E IN A IR FLOW
......... ...... T ..............
L IT T L E OR NO C H A N G E IN A IR FLOW
N O R M A L A IR FLOW
LOW OR NO A IR FLOW
Check heater o u tle t tem pe ra ture
w ith 2 2 0 ° F range th e rm o m e te r.
(a p p ro x im a te o u tle t a ir tem peratures)
O u tle t A ir 145 150 155
165
A m b ie n t A ir 0 25 40 75
N O R M A L T E M P E R A T U R E
Remove a ll o b s tru c tio n s under fr o n t seat.
Car does n o t b u ild up heat - operate ve nt
c o n tro ls a nd see th a t th e a ir vent doo rs
close c o m p le te ly , if n o t, adjust.
LOW T E M P E R A T U R E
HZ
(C heck th e system tem pe ra ture a fte r re­
p a irin g th e ite m checked to c o m p le te the
diagnosis.)
X
Check c o o la n t level; if lo w , f ill. L o o k fo r
or feel a ll ra d ia to r and heater hoses and
co n n e ctio n s fo r leaks. Repair o r replace.
Check th e ra d ia to r cap fo r damage and re­
place if re q uired .
X
Check heater a nd ra d ia to r hoses fo r kin ks
straighten and replace as necessary.
Check te m p e ra tu re d o o r fo r m ax heat po­
sitio n . A d ju s t if necessary.
[
H E A T E R CORE
r
| Feel tem peratures o f heater in le t and o u tle t hoses,
j
W A R M IN L E T A N D O U T L E T HOSES
X
i Check engine th e rm o s ta t.
H O T IN L E T A N D W A R M O U T L E T HOSES
......:.... .................— ~
Check p u lle y s , belt ten sio n, etc., fo r p ro ­
per o p e ra tio n . Replace o r service as neces­
sary.
.................. i . ~xz
Remove hoses fro m heater core. Reverse
flush w ith tap w ater. I f plugged, repair or
replace.
LOW A IR FLOW
Check heater o u tle t fo r o b s tru c tio n - re­
move.
Check m o to r voltage a t closest m o to r line
co n n e c tio n w ith a v o ltm e te r.
U N D E R 10 V O L T S O V E R 10 V O L T S
Check b a tte ry v o lts - u nder 10 vo lts,
recharge then recheck m o to r voltage.
Check w irin g a nd co n n ectio n s fo r
under 10 v o lts fro m m o to r to fan
sw itch . Repair or replace last p o in t
o f u nd er 10 v o lt reading.
A p p ly e xte rn a l g ro un d, (ju m p e r w ire) to
m o to r case. IN C R E A S E D A lR FLOW -
re p a ir ground.
SAM E A l R F L O W - rem ove m o to r and
check fo r o b s tru c tio n in system open­
ing. I f none, R E P LA C E M O T O R . If
o b s tru c tio n , rem ove m aterial and re­
in stall m o to r.
**C h e c k s h u to ff d o o r p o s itio n fo r fu ll
system a ir flo w . A d ju s t if necessary.
NO A IR FLOW
CHECK FUSE
FUSE B LO W N - replace fuse.
A IR FLOW - system o kay.
BLOWS FUSE
Remove p o sitive lead fro m m o to r and
replace fuse.
FUSE R E M A IN S O K - rem ove m o to r
and check fo r o b s tru c tio n in system
opening, if none, R E P LA C E M O TO R .
If o b s tru c tio n , rem ove m a terial and
re -in s ta ll m o to r.
BLOWS FUSE - check fo r shorted
w ire in b lo w e r e lectric c ir c u it -
See Heater C ir c u it D ia g no stic C hart.
FUSE OK
FUSE O K - See Heater C irc u it
D iagnostic C hart.
‘ C H E C K F OR C-K M O D E L S
O N L Y
" C H E C K F O R G M OD E L S
O N L Y