A/C and Blower Issue

[rmwilliams]

I have a 96 XLT, with the 4.0 pushrod.

Lately I've noticed that when the A/C is on "Max A/C" and I accelerate and put a load on the engine, the cold air starts blowing out of the defrost vents on the dashboard. Once I'm back to cruising, the cold air will begin to blow out of the proper vents. To avoid this problem, I have it on "A/C" rather than Max A/C. Any one experiencing this? If so, what's the solution? Is it a bad relay?? How do I fix it?

 

[MrShorty]

I'm not real sure on this, but aren't the ventilation controls run by engine vacuum? If so, I believe there is supposed to be a check valve in the vacuum line from the engine compartment to help regulate the ventilation controls. Maybe it's stuck open or something and when you stomp on the pedal, engine vacuum goes down, and causes a change in the ventilation controls. Again I'm not real sure on this. Someone else may chime in with something more certain.

 

[Robert]

Yes, this same issue was brought up a week or two ago. Do a search and you should find a lot of information regarding it. Your A/C - heater doors default to the Defrost position when a fault is detected (such as a loss in vacuum). This is done so that you should always have working windshield defrosters. All of the blend doors are actuated by a vacuum controlled solenoid. If vacuum is lost, the doors go to their default position. There is a check valve in the system that is supposed to maintain vacuum. If it leaks vacuum won't be maintained so every time you accelerate your doors will go to their default position. They will return to their previous position when the vacuum resumes. The person that started the last thread found a hose disconnected behind his A/C controls. Any leaks in the vacuum system downstream from the check valve will cause this.

 

[rmwilliams]

Thanks. This makes a little bit of sense now. I replaced my water pump back in late May. As a consequence I had to disconnect hoses for access. I did find that one hose was not pluged back in after the fact, but not sure if that solved the problem or not. I will re-check all the hoses to make sure vacuum is maintained.

 

[rmwilliams]

I rechecked the hoses and found that my hose clamp wasn't secured properly. When I stomped on the pedal I suspected that the vacuum dropped and that was creating the problem with the A/C coming out of the defroster vents. I'm good to go now!

 

[Robert]

Glad to have helped.