As the title says, I'm having problems with the heater control position selector.. It's stuck in the defrost position no matter what position I turn it to. The vehicle is an 00 Cherokee. I know that the position selector is vacuum controled but i'm unsure of how to test it or really how the whole thing works. I have done a search and all I have come up with is someone with a 91 XJ who had a similar issue but his was mechanically controlled. I'm wondering is this is a common problem and how do I test and fix it?

 

Pull the **** off is it cracked or stripped.

 

No, the **** is fine.

 

Just saying I had a similar issue thought the same.problem on m tj. Pulled the **** off and was suprised to see it cracked but when I turned it it felt very good like it was moving the shaft. Just figured since u had the same **** it could b a similar problem

 

I did check that. When you turn the **** it works fine, it goes through all the positions just fine. It just doesn't come out of anywhere but the defrost. It switches to the off position and actually goes off.

 

It's a vacuum leak most likely a leaky vacuum ball but could be a line in the system.

 

for Reference Only:
On a '96 there's a skinnnnny little hard plastic tube behind the battery along the inside wheel well metal that goes to the vacuum canister behind the front bumper - it was crushed apart on mine. I took a short length of rubber hose and hose clamped it back together - works just fine now.

Check all the other larger soft rubber hoses up near the firewall and the other skinny one with a fat elbow that plugs into something else up there too.