2000 1500 Ram 4x4. When I have air set at the dash vents and go up any kind of upgrade on the highway it switches to defrost until I am past the hill. When the engine is no longer laboring it switches back to my vents. help?

 

You have a vacuum leak in a check valve or hose that comes off your intake manifold. When you go up the hill your vacuum decreases and it defaults to defrost. On the passenger side of the intake are a bunch of vacuum hoses check these for cracks or if any are disconnected. There are a couple check valves in the hoses as well between the intake and the firewall.

 

Thank you!! I will check it out.

 

Impressive!! You were exactly right. One of the hoses was barely holding on. Thanks!!

 

Any time. Glad you found it.