Questionthe air is coming from the vents and then it stops and comes out on the top where the deforst comes from and then the check engine light comes on
AnswerJudith,
What type of buick are we talking about?
Well, no matter, the answer will be generally the same.
Your directional doors are controlled by vaccuum. With no vaccuum being pulled, the default position is at the defrost outlets. This is standard for every vehicle made. This default position is in case your system should go out in the middle of the winter, you would still be able to defrost and defog your windshield.
The way it works,
Your vaccuum source normally is generated from either your brake booster diaghram or your intake manifold. This line connects to a vaccuum harness connector that contains valves that route the vaccuum to different lines that go to the individual doors in your ventilation system. This connector also recieves an electrical signal from your control head that tells it which valves to vent and vaccuum dependant upon where you set the selector switch.
Being that yours goes to the default position AND your check engine light comes on, I believe the problem lies in your car itself not the A/C. My opinion (not a vehicle mechanics expert) would be that your brake booster may be having a problem, or the diaghram inside it is beginning to leak.
I would highly recommend you have this taken to a shop to get looked at. Mainly because if it is a problem with your brake booster, it could become a safety issue before too long. Should it go bad, I do not believe you will lose your brakes, but you will have to exert more strength to the pedal to stop your vehicle.
So, in closing, I do not believe this is an A/C issue, because it would not cause your check engine light to come on if it was isolated to the A/C ventilation doors. Please have your car checked.
Thank you for the question, I hope I was of some assistance. If I can do anything further during this process, or in the future, please do not hesitate to ask. If you found this response to be of some assistance, please remember to rate this answer. Thanks again and good luck in everything.
