Hi, my name is Ben,

I have a 1997 Dodge Ram Van, it has around 129,000 miles.

The A/C runs fine and then it switches to defrost, blowing cold air out of the defrost. Anyone have any idea what the problem is?

Ben

 

The HVAC unit is regulated by the vacuum system of the van. If you pull off the dash cover near the controls or above the glove-box. (can't remember which on your model year) you will find a bunch of colored tubing going to a selector valve. Follow each tube or put pressure in the tube to see which one is leaking. If you find it, then trace that tube and patch the leak.

Usually, the leak is at the selector valve or the other end.

OR, it's very possible that you have a vacuum leak about the engine that needs to be addressed to correct the problem. Checking all the vacuum hoses would be a great idea on an old van like yours.

 

On the 97 look on the passenger side of the intake manifold and follow the vacuum line down to the vacuum ball behind the passenger headlamp. Then follow the rest of the line up over the PCM to the firewall. Many times these nylon vacuum lines get brittle from the engine heat and age. Look for any breaks or cracks in that line and to fix it cut the line and insert the line into a piece of 1/8 vacuum rubber hose.