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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Astro - 4WD 🢒 HVAC 🢒 HVAC Systems - Manual 🢒 Heating Performance Diagnostic

Heating Performance Diagnostic Auxiliary System

Step

Action

Yes

No

DEFINITION: Heating system performance of the auxiliary heater.

1

Were you sent here from Symptoms or another diagnostic table?

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

2
  1. Start the engine.
  2. Allow the engine to idle.

Does the engine reach a normal operating temperature?

Go to Step 3

Go to Step 10

3

    Caution: Refer to Moving Parts and Hot Surfaces Caution in the Preface section.

  1. Allow the engine to idle.
  2. Select the maximum auxiliary temperature setting.
  3. Select the minimum auxiliary blower speed.
  4. Feel the temperature of the inlet and outlet heater hoses.

Does the inlet heater hose feel warmer than the outlet heater hose?

Go to Step 4

Go to Step 5

4
  1. Allow the engine to idle.
  2. Select the minimum auxiliary blower speed.
  3. Select the warmest auxiliary temperature setting.
  4. Feel the temperature of the inlet and outlet heater hoses to the auxiliary heater core.

Does the inlet heater hose feel warmer than the outlet heater hose?

Go to Step 8

Go to Step 5

5
  1. Install a thermometer into an auxiliary air outlet.
  2. Secure a thermometer on the outlet heater hose of the auxiliary heater core.
  3. Select the maximum auxiliary blower speed.
  4. Select the warmest auxiliary temperature setting.
  5. Record the temperature at the following locations:
    6. • The auxiliary air outlet
    • The auxiliary heater core outlet hose
  6. Compare the recorded temperatures.

Are the two temperature readings about equal?

Go to Step 6

Go to Step 7

6
  1. Inspect the following areas of the vehicle for cold air leaks:
    2. • The auxiliary HVAC module case
    • The auxiliary air ducts
  2. Perform any necessary repairs.

Is the repair complete?

Go to Step 12

--

7

Inspect the auxiliary HVAC module for correct temperature door operation. Refer to Symptoms - HVAC Systems - Manual .

Does the temperature door operate correctly?

Go to Step 12

Go to Step 11

8
  1. Turn OFF the engine.
  2. Backflush the auxiliary heater core.
  3. Start the engine and allow the engine to idle.
  4. Select the minimum auxiliary blower speed.
  5. Select the warmest auxiliary temperature setting.
  6. Feel the temperature of the inlet and outlet heater hoses at the auxiliary heater core.

Does the inlet heater hose feel warmer than the outlet heater hose?

Go to Step 9

Go to Step 12

9

Replace the auxiliary heater core. Refer to Heater Core Replacement .

Is the repair complete?

Go to Step 12

--

10

Repair the low engine temperature concern. Refer to Engine Fails To Reach Normal Operating Temperature in Engine Cooling.

Is the repair complete?

Go to Step 12

--

11

Repair the temperature door operation.

Is the repair complete?

Go to Step 12

--

12

Operate the system in order to verify the repair.

Did you find and correct the condition?

System OK

Go to Step 2

Heating Performance Diagnostic Front System

Step

Action

Yes

No

DEFINITION: Heating system performance.

1

Were you sent here from Symptoms or another diagnostic table?

Go to Step 2

Go to Symptoms - HVAC Systems - Manual

2
  1. Start the engine.
  2. Allow the engine to idle.

Does the engine reach a normal operating temperature?

Go to Step 3

Go to Step 9

3

    Caution: Refer to Moving Parts and Hot Surfaces Caution in the Preface section.

  1. Allow the engine to idle.
  2. Select the warmest temperature setting.
  3. Select the minimum blower speed.
  4. Select the OFF position for the auxiliary heating system, if equipped.
  5. Feel the temperature of the heater inlet and outlet hoses.

Does the inlet heater hose feel warmer than the outlet heater hose?

Go to Step 8

Go to Step 4

4
  1. Allow the engine to idle.
  2. Select the FLOOR mode.
  3. Select the minimum blower speed.
  4. Select the warmest temperature setting.
  5. Feel the temperature of the inlet and outlet heater hoses to the heater core.

Does the inlet heater hose feel warmer than the outlet heater hose?

Go to Step 8

Go to Step 5

5
  1. Install a thermometer into the center I/P PANEL air outlet.
  2. Secure a thermometer to the heater core outlet hose.
  3. Select the PANEL mode.
  4. Select the maximum blower speed.
  5. Select the warmest temperature setting.
  6. Record the temperature at the following locations:
    7. • The center I/P PANEL air outlet
    • The heater core outlet hose
  7. Compare the recorded temperatures.

Are the two temperature readings about equal?

Go to Step 6

Go to Step 7

6
  1. Inspect the following areas of the vehicle for cold air leaks:
    2. • The cowl
    • The recirculation door
    • The HVAC module case
  2. Perform the necessary repairs.

Are the repairs complete?

Go to Step 11

--

7
  1. Inspect the temperature door operation. Refer to Symptoms - HVAC Systems - Manual .
  2. Perform any necessary repairs.

Is the repair complete?

Go to Step 11

--

8
  1. Turn OFF the engine.
  2. Backflush the heater core.
  3. Start the engine and allow to idle.
  4. Select the FLOOR mode.
  5. Select the minimum blower speed.
  6. Select the warmest temperature setting.
  7. Feel the temperature of the inlet and outlet heater hoses at the heater core.

Does the inlet heater hose feel warmer than the outlet heater hose?

Go to Step 10

Go to Step 11

9

Repair the low engine temperature concern. Refer to Engine Fails To Reach Normal Operating Temperature in Engine Cooling.

Is the repair complete?

Go to Step 11

--

10

Replace the heater core. Refer to Heater Core Replacement .

Is the repair complete?

Go to Step 11

--

11

Operate the system in order to verify the repair.

Did you find and correct the condition?

System OK

Go to Step 2