GMC 1982 Light Duty Truck Service Manual page 29

1A-4 HEATER
Temperature o f heater a ir a t o u tle ts too low to heat up pas­
senger compartment.
Temperature o f heater a ir a t o u tle ts adequate but the v e h i c l e
w i ll not b u ild up s u f f ic ie n t heat.
Inadequate d e fro s tin g a c tio n .
Inadequate c ir c u la tio n o f heated a i r through v e h i c l e .
E r r a tic heater o p e ra tio n .
Hard o p e ra tin g o r broken c o n tro ls .
DIAGNOSIS
TROUBLE CAUSE AND CORRECTION
1. See " In s u f f ic ie n t Heat D iagnostic C h a rt".
Check fo r body leaks such as:
1. F loor side kick pad v e n tila to r s p a r t ia lly open.
2. Leaking grommets in dash.
3. Leaking welded seams along rocker panel and w in d sh ie ld .
4. Leaks through access holes and screw holes.
5. Leaking rubber molding around door and windows.
6. Leaks between se a ling edge o f blower and a ir in l e t assembly
and dash, and between se a lin g edge o f heater d is tr ib u t o r
assembly and dash.
1. Check th a t DEFROST le v e r com pletely opens d e fro s te r door
in DEF p o s itio n - A d ju st i f necessary.
2. Insure th a t temperature and a ir doors open f u l l y - A d ju st.
3. Look fo r o b s tru c tio n s in d e fro s te r ducts - Remove any
o b s tru c tio n s .
4. Check fo r a ir leak in du cting between d e fro s te r o u t le t on
heater assembly and d e fro s te r duct under instrum ent panel -
Seal area as necessary.
5. Check p o s itio n o f bottom o f nozzle to heater lo c a tin g tab -
A d ju s t.
6. Check p o s itio n o f d e fro s te r nozzle openings r e la tiv e to in s tr u ­
ment panel openings. Mounting tabs provide p o s itiv e p o s itio n
i f p ro p e rly in s ta lle d .
1. Check heater a i r o u t le t fo r c o rre c t in s t a lla t io n - R e in s ta ll.
2. Inspect f lo o r ca rp e t to in su re th a t ca rp e t lie s f l a t under
f r o n t seat and does not o b s tru c t a i r flo w under seat, and
also in sp e ct around o u t le t ducts to in su re th a t ca rp e t is
w ell fastened to flo o r to prevent cupping o f a i r flo w - C orrect
as necessary.
1. Check co o la n t le v e l - F i l l to proper le v e l.
2. Check fo r kinked heater hoses - r e lie v e kinks o r replace hoses.
3. Check o p e ra tio n o f a ll bowden cables and doors - A djust as
necessary.
4. Sediment in heater lin e s and r a d ia to r causing engine thermo­
s ta t to s tic k open - flu s h system and clean o r replace thermo­
s ta t as necessary.
5. P a r t ia lly plugged heater core - ba ckflush core as necessary.
1. Check fo r loose bowden cable tab screws o r m is-a d ju sted bowden
cables - C orrect as re q u ire d .
2. Check fo r s tic k in g heater system d o o r(s) - L u b rica te as required
using a s ilic o n e spray.