GM Service Manual Online
For 1990-2009 cars only
  1. Inspect for an obstruction in both of the defroster nozzles.
  2. Perform the following steps, as necessary:

    • Remove any foreign objects.
    • Repair any loose instrument panel pad that blocks an outlet.
  3. Inspect for the proper operation of the defroster air valve.
  4. Inspect for one of the following conditions.
  5. Replace the defroster vacuum actuator or hose if one of the following conditions exist:

    • A faulty defroster air valve vacuum actuator
    • Refer to Defroster Valve Actuator Replacement .
    • A faulty defroster air valve vacuum hose
    • Refer to Vacuum Hose Harness Replacement .
  6. Inspect for insufficient heating.
  7. Refer to Heating Insufficient .