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defrost on 1999 gmc sonoma?
The heat/ac vents on my truck do not switch from the dash vents to floor or defrost. No matter where the selector switch is. Any ideas as to what it could be?
1 Answer
- ?Lv 78 years agoFavorite Answer
Heater/AC vent doors under the dash are operated by vacuum from the engine. With your 15-year-old truck, it's possible that a vacuum line (small diameter rubber hose) has come loose from the engine or one of the heater control door motors, and is not allowing the system to function as it should.