Chevrolet LIGHT DUTY TRUCK (SERIES 10-35) Service Manual page 29

1A-4 HEATER
TROUBLE
Temperature of heater a i r at ou tle ts too low to heat up pas­
senger compartment.
Temperature o f heater a i r at ou tle ts adequate but the
w i l l not build up s u f f i c i e n t heat.
Inadequate defrosting action.
Inadequate c i r c u l a t i o n of heated a i r through
Erratic heater operation.
Hard operating or broken c on trols.
LIG H T TR U CK SERVICE MANUAL
DIAGNOSIS
1. See " I n s u f f i c i e n t Heat Diagnostic Chart".
vehicle
Check for body leaks such as:
1. Floor side kick pad v e n t i la t o r s p a r t i a l l y open.
2. Leaking grommets in dash.
3. Leaking welded seams along rocker panel and windshield.
4. Leaks through access holes and screw holes.
5. Leaking rubber molding around door and windows.
6. Leaks between sealing edge o f blower and a i r i n l e t assembly
and dash, and between sea ling edge of heater d i s t r ib u t o r
assembly and dash.
1. Check that DEFROST lever completely opens defroster door
in DEF po s itio n - Adjust i f necessary.
2. Insure that temperature and a i r doors open f u l l y - Adjust.
3. Look fo r obstr uctions in d efroster ducts - Remove any
o b s t r u c t i o n s .
4. Check for a i r leak in ducting between defroster o u t le t on
heater assembly and defroster duct under instrument panel -
Seal area as necessary.
5. Check p osition o f bottom of nozzle to heater lo cat ing tab -
Adjust.
6. Check p osition of defroster nozzle openings r e la t i v e to i n s t r u ­
ment panel openings.
i f properly in s t a lle d .
vehicle.
1. Check heater a i r ou tle t for cor re ct i n s t a l l a t i o n - R e i n s t a ll .
2. Inspect f lo o r carpet to insure that carpet l i e s f l a t under
fro nt seat and does not obstr uct a i r flow under seat, and
als o inspect around ou tle t ducts to insure that carpet is
well fastened to f lo o r to prevent cupping of a i r flow - Correct
as necessary.
1. Check coolant level - F i l l to proper le ve l.
2. Check f o r kinked heater hoses - re lie v e kinks or replace hoses.
3. Check operation of a ll bowden cables and doors - Adjust as
necessary.
4. Sediment in heater li n e s and ra d iator causing engine thermo­
sta t to s t i c k open - f lu sh system and clean or replace thermo­
sta t as necessary.
5. P a r t i a l l y plugged heater core - backflush core as necessary.
1. Check for loose bowden cable tab screws or mis-adjusted bowden
cables - Correct as required.
2. Check for s t i c k i n g heater system door(s) - Lubricate as required
using a s i l i c o n e spray.
CAUSE AND CORRECTION
Mounting tabs provide p o s itiv e position