GM Service Manual Online
For 1990-2009 cars only

Step

Action

Yes

No

1

Was the Function Test performed?

Go to Step 2

Go to Function Test

2

  1. Set the mode to VENT.
  2. Set the temperature control to full COLD.
  3. Set the blower speed to HIGH.
  4. Inspect for airflow at the vent, heater, defroster, and side window defroster outlets.

Is there airflow through the vent outlets at ambient temperature and no airflow through the heater, defroster and side window defroster outlets?

Go to Step 3

Go to Step 5

3

  1. Set the mode to HEAT.
  2. Set the temperature control to full HOT.
  3. Inspect for airflow at the vent, heater, defroster and side window defroster outlets.

Is there hot airflow through the heater outlet at the blower high speed, minimum of hot airflow through the defroster and the side window defroster outlets and no airflow at the vent outlets?

Go to Step 4

Go to Step 5

4

  1. Set the mode to DEFROST.
  2. Inspect for airflow at the vent, heater, defroster and side window defroster outlets.

Is there hot airflow through the defroster outlet and the side window defroster outlets at the blower at high speed, minimum hot airflow through the heater outlet and no airflow at the vent outlets?

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Go to Step 5

5

  1. Disconnect the affected control cable(s) at the heater case.
  2. Inspect the door travel and effort.

Are the door travel and effort correct?

Go to Step 6

Go to Step 8

6

Test the control cable(s) travel by moving the corresponding control at the heater control unit.

Is the control cable travel correct?

Go to Step 7

Go to Step 9

7

Inspect the control cable(s) attachment at the heater control unit. Repair as necessary. Refer to Control Assembly Replacement .

Is the repair complete?

Go to Function Test

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8

Repair the affected door at the heater case as necessary. Refer to Heater Case Replacement .

Is the repair complete?

Go to Function Test

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9

Repair or replace the affected control cable(s) as necessary. Refer to the following:

    • Temperature Control Cable Replacement
    • Vent Control Cables Replacement

Is the repair complete?

Go to Function Test

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