Hey guys, I’m new to this forum, I have a 1995 Dodge ram 2500 12 valve cummins. A few days ago i went to turn on my ac and it was only blowing through the defrost mode no matter what position i put the switch in. My dash cover is almost gone so i was able to see just about every vacuum line coming from the switch and none of them were popped off or cracked. I also checked the vacuum lines in the engine bay and they are good as well, what could be the issue?

 

You’re gonna have to trace your vacuum lines thoroughly. It defaults to defrost mode when vacuum is lost. Check all your vacuum lines coming from the vacuum pump up to the firewall and across. And then check your vacuum lines under the dash from the floorboards

 

Also check the switch itself, and the vacuum actuators (its unlikely that they would all have failed diaphragms, but you never know) - you can use a hand vacuum pump for this

 

When mine defaulted to the dash vents the vacuum line that goes over the top of the engine (originally could be on the firewall) had a leak. I would get a vacuum pump and start eliminating possibilites.

Bob