Diagnosis Of The Heater System - GMC G Service Manual

DIAGNOSIS OF THE HEATER SYSTEM

Problem
Temperature of Heater
Air at the Outlets Is
Too Low to Heat Up
Passenger
Compartment
1.
Temperature of Heater
Air at the Outlets is 2.
Adequate but the 3.
Vehicle Will Not Build
Up Sufficient Heat 4.
5.
6.
Inadequate Defrosting 1.
Action
2.
3.
4.
5.
6.
1.
Inadequate
Circulation of Heated
2.
Air Through the
Vehicle
Erratic Heater 1.
Operation 2.
3.
4.
5.
1.
Hard Operating or
Broken Controls
2.
Possible Cause
Refer to "Insufficient Heat Diagnosis."
Floor side kick pad ventilators partially open.
Leaking grommets in dash.
Leaking welded seams along the rocker
panel and windshield.
Leaks through the access holes and screw
holes.
Leaking rubber molding around the door and
windows.
Leaks between the sealing edge of blower
and the air inlet assembly and cowl, and be­
tween the sealing edge of the heater distribu­
tor assembly and cowl.
Check that the DEFROST lever completely
opens the defroster door in the DEF position.
Insure that the temperature and air doors
open fully.
Look for obstructions in the defroster ducts.
Check for air leak in the ducting between the
defroster outlet on heater assembly and the
defroster duct under the instrument panel.
Check the position of the bottom of the
nozzle to the heater locating tab.
Check the position of the defroster nozzle
openings relative to instrument panel open­
ings. Mounting tabs provide positive position
if properly installed.
Check the heater outlet for correct
installation.
Inspect the floor carpet to insure that the
carpet lies flat under the front seat and does
not obstruct air flow. Also inspect around the
outlet ducts to insure that the carpet is well
fastened to floor to prevent cupping of the air
flow.
Check the coolant level.
Check for kinked heater hoses.
Check the operation of all bowden cables
and doors.
Sediment in the heater lines and radiator
causing the engine thermostat to stick open.
Partially plugged heater core.
Check for loose cable tab screws or misad-
justed, misrouted or kinked cables.
Check for sticking heater system door(s).
HEATING 1A-7
Correction
Refer to "Insufficient Heat Diagnosis."
1. Check and adjust.
2. Reseal or replace.
3. Clean and rewash.
4. Reseal or replace.
5. Reseal or replace.
6. Reseal or replace.
1. Adjust if necessary.
2. Adjust.
3. Remove any obstructions.
4. Seal area as necessary.
5. Adjust.
6. Adjust the defroster nozzle openings.
1. Remove and install.
2. Correct as necessary.
1. Fill to the proper level.
2.
Relieve kinks or replace hoses.
3. Adjust as necessary.
4. Flush the system and clean or replace ther­
mostat as necessary.
5. Backflush core as necessary.
1. Correct as required.
2. Lubricate as required using a silicone spray.
GMTB-0840-2L