1999 Ram 1500


My ram 1500 4x4 automatic when the a/c is on and I give it gas or under a load the a/c shift to the defroster I let up on the gas and it return to the a/c, can anyone help me with one?


You have a vacuum leak someplace in the A? system. Look under the hood to see it there is possibly a round canister with 2 small hoses coming out of it. I know Fords and Chevys have them. This could be the problem.

This little tank is usually a type of regulator so to prevent you problem on acceleration.


I’m sorry i’m not much of a mechanic I probably sound stupid but what is the A?


It also could be a bad check valve.

The dampers/doors that direct airflow for the heating system are run by actuators powered by engine manifold vacuum. The problem is that the when you increase engine load, such as accelerating or going up a hill, engine vacuum decreases, and it may be dropping enough to affect the damper’s opperation. There should be a check valve in the vacuum line that feeds the heating system control unit. If this valve fails it will cause the symtoms you describe.

Also, ask the dealer to check for TSBs on this; I seam to reacal this being a common problem for Chrysler and may require the addition of a vacuum canister.