Diagnostic Aids

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The condition may be intermittent. Refer to TESTING WIRING SYSTEMS FOR INTERMITTENT & POOR CONNECTIONS in Wiring Systems.
Inspect the air delivery system for the following conditions:
- A dirty HVAC air filter, if applicable
- An obstruction to the airflow
- Air leaks
- Misaligned air ducts
- Broken or binding linkages or doors
Fig 1: Diagnosis Procedure Air Delivery Improper
Courtesy of GENERAL MOTORS CORP.