The blend door on my 1999 RAM 1500 club cab swings to the heat position all by itself when I am using the AC. Then it will swing back to allow cool air from the AC for a while then you hear a thump and the blend door has swung back to send air from the heater core. Can anyone tell me why this is happening?

 

I have the same problem with mine. It does that and it also switches from pannel to floor to defrost like it has its own mind. I was told that the doors work of a vacuum and that my lines could have a leak. This seems to make sense because I can cut it to the off posistion and then back on and it does what its told for a few mins till it has its next random spasm. Its extremely anoying and when my mechanic fixes my plenum plate in a few weeks he said he would take a look and possible fix it. I post what he says the reson is on here after that but I am guessing its a leak in the vacuum lines.

 

Thanks for sharing your information with me. I also feel it is a vacumm leak. I just don't know where to look. I will wait to hear what your mechanic tells you regarding your problem. Thanks again. If you have problems with your cruise control not holding speed I will tell you how I fixed mine. The cruse control servo is located under the battery. There is a vaccum hose that connects to this servo. There was a hole in the vaccum hose underneath the battery because it was rubbing against another hose. I cut out the part with a hole and used drip irrigation line to splice the vaccum line and just used electrical tape at both ends and now my cruise works great