A/C works intermittenly

My A/C has gone mad. It sometimes blows thru the front vent, sometimes the defrost, sometimes the lower vent–no matter what I have it set to. It does work, I just can’t control where it comes out. My regular mechanic said it seems like something is stuck in the system and that the dealer would have to pull out the dashboard to fix it–sounds like a nightmare. Here is the really curious thing: When it does decide to blow through the front vents as I have it set, it always does so right after I have been cruising at a good speed and then I have to brake for a light. Could this be some sort of faulty switch? Who do I have fix it–an A/C specialist, or the dealer?

It sounds like a vacuum problem to me.

You have a vacuum leak in the blend door system. When you suddenly let up on the accelerator the engine vacuum will rise. This will overcome the vacuum loss and the doors will operate until the engine vacuum drops. Find the leak and your problem is solved.

This is great advice! So, is that something I can describe to my regular mechanic (a great shop I have used for 11 years), or is that something only an A/C specialist can fix? Forgive my ignorance–I just don’t know where to go!

Your mechanic should have no problem fixing this malfunction. An AC specialist is not needed.

I am thrilled to have a solution–it’s in the 90s here and I need AC! Thanks so much. I will take it in and give my mechanic this info and I’m sure he can fix it now. Thanks again.