1999 Doge Ram 1500 Van. It had to happen on one of the hottest day of the year. My air control went crazy. Direction of flow changes auto, mostly to windshield. Direction seems to shift as per speed as well.
Can someone shed light on this issue(s)?

Thanx in advance

 

It's a loss of steady/strong vacuum to the HVAC controls. The HVAC vacuum line comes off of the intake manifold on the passenger side. Start there and follow it to find the leak. Also, a few inches from the intake in the vacuum line is a one-way check valve. If this valve leaks and allows air to flow in both directions, then it is the source of your problem.

 

That is a vacuum issue for sure. Windshield is the default setting, if no vacuum is applied. Your controls are not changing according to speed, but rather engine vacuum. When engine vacuum becomes too low, the controls default to windshield.

Are you having problems with the heat coming on when it is not supposed to as well?

 

Greatly appreciate your time and efforts, both of u!
Will check it out 2moro morning & keep you posted as I may need further assistance from you guys.

Thanx again!

 

I tested suction end on the hvac, located at the foot of passenger. There is suction as smoke got sucked in but nothing like before when plastic bag would get sucked right in.
Since there is very very low suction, I guess there is a leak somewhere as posted by 2 members above. *Is this correct?

 

The vacuum line I mentioned above runs behind the passenger headlight. That's where you will find the vacuum reservoir. It's time to just start checking for that leak.

 

I have the same problem and I still can't find a vacuum line leak....it is driving me nuts!! I'm doing a tune up this week so the doghouse will be out for a while, maybe I'll get lucky

 

Tracking down small vacuum leaks can be very trying if they aren't loud enough to overcome the roar of the engine. The solution is to remove the main vacuum line from the intake manifold and attach a hand vacuum pump (brake bleeder). They are about $35 and will come in handy later for other repairs. I have also successfully used a large plastic syringe but it was difficult.

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