GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Astro - 2WD 🢒 HVAC 🢒 Heating, Ventilation and Air Conditioning 🢒 Defrosting Insufficient

Step

Action

Value(s)

Yes

No

1

Test the cooling system for the following conditions:

    • Cooling system leaks
    • Low coolant level
    • Loose or worn belt
    • Leaking or kinked heater hoses
    • Loss of radiator cap pressure seal

Repair the cooling system as necessary.

Is the repair complete?

--

Go to Step 2

--

2
  1. Adjust the heater controls to the following settings:
    2. • HEATER mode
    • HIGH blower
    • Full WARM
  2. Turn ON the ignition switch.
  3. Inspect the airflow out of the floor air outlet.
  4. Inspect the outlet attachment.

Is the airflow high?

--

Go to Step 3

Go to Step 11

3

Check the blower speeds for changes in the airflow .

Do the blower speeds change?

--

Go to Step 4

Go to Step19

4

Perform the heater output temperature check.

Is the heater output temperature low?

--

Go to Step 20

Go to Step 5

5

Close the temperature valve.

Is the temperature valve closed?

--

Go to Step 6

--

6

Turn the temperature rotary knob to full HOT.

Is the temperature valve fully closed?

--

Go to Step 7

Go to Step 25

7
  1. Start the vehicle with the temperature valve on full WARM.
  2. Inspect the temperature of the heater inlet and outlet hoses.

Is the air temperature around both hoses equal to or greater than the specified value?

85°F (24°C)

Go to Step 8

Go to Step 27

8
  1. Remove the hoses at the heater core.
  2. Inspect the hoses for proper installation.

Are the hoses properly installed?

--

Go to Step 9

Go to Step 24

9
  1. Backflush the heater core.
  2. Drain the heater core.
  3. Replace the coolant.
  4. Retest the hose temperature.

Are both hoses warm?

--

Go to Step 10

Go to Step 26

10

Replace the heater core. Refer to Heater Core Replacement .

Is the repair complete?

--

Go to Heater Blower Controls System Check

--

11

Perform the functional test. Refer to Function Test .

Did you find and correct the condition?

--

Go to Heater Blower Controls System Check

Go to Step 12

12

Check the air flow from the defroster and vent outlets.

Is the airflow high?

--

Go to Step 21

Go to Step 13

13
  1. Move the mode lever to DEFROST.
  2. Test the airflow.

Is the air flow high?

--

--

Go to Step 14

14

Check the blower speeds for airflow change.

Do the speeds change?

--

Go to Step 15

--

15

Inspect the blower at the blower inlet and the plenum for airflow obstructions.

Are the blower inlet and the plenum free of obstructions?

--

Go to Step 16

--

16
  1. Turn the blower on HIGH.
  2. Turn the temperature rotary knob from full HOT to full COLD. Listen for an airflow change.

Did the airflow change?

--

Go to Step 17

Go to Step 18

17

Inspect the system for airflow obstructions between the blower and the system outlets.

Did you find and remove any obstructions?

--

Go to Heater Blower Controls System Check

--

18

Inspect the following components:

    • The temperature valve
    • The control assembly
    • The harness

Did you find and repair a condition?

--

Go to Heater Blower Controls System Check

--

19
  1. Inspect the following components:
    2. • The blower switch
    • The resistor assembly
    • The wiring harness.
  2. Repair the components as necessary.

Is the procedure complete?

--

Go to Step 5

--

20
  1. Inspect the vehicle for cold air leaks at the following components:
    2. • The cowl
    • The heater case
    • The vents
  2. Inspect under the seat for obstructions.

Are the components clear of obstructions?

--

Go to Heater Blower Controls System Check

--

21

Move the defroster and/or vent valve to the HEATER mode.

Is the defroster airflow correct?

--

Go to Step 22

--

22
  1. Remove the floor air outlet.
  2. Inspect the outlet for obstructions.

Does the air speed remain constant?

--

Go to Step 23

Go to Step 15

23
  1. Inspect the following components:
    2. • The blower switch
    • The resistor assembly
    • The wiring harness
  2. Repair any components as necessary.

Is the repair complete?

--

Go to Step 6

--

24

Properly install the hoses.

Is the installation complete?

--

Go to Step 1

--

25
  1. Re-index the temperature cable.
  2. Check the following items:
    3. • The temperature valve adjustment
    • The cables
    • The linkage

Is the repair complete?

--

Go to Heater Blower Controls System Check

--

26
  1. Retest the system.
  2. Verify the symptoms.

Is the repair complete?

--

Go to Heater Blower Controls System Check

--

27
  1. Inspect the thermostat for proper installation.
  2. Inspect for correct seating.

Are the installation and seating correct?

--

Go to Step 28

Go to Step 29

28

Replace the thermostat.

Is the repair complete?

--

Go to Heater Blower Controls System Check

--

29
  1. Re-install the thermostat.
  2. Retest the system.

Is the repair complete?

--

Go to Heater Blower Controls System Check

--