Hi all. My wife has a 1996 jeep cherokee. The normal HVAC controls have the slider which activates both the vents and the AC. For whatever bizarre reason, the slider no longer toggles the vents away from "defrost". You can put it in any position, and the vents don't move to the dash or the floor. The AC works (which also fogs up the windshield).

I replaced the heater control valve. There's a device to the left which is making a hissing noise. Is this supposed to be hissing? What's the name of it?

Ideas?

 

check for a vacuum leak in one of your lines, that could be the cause for a lack of hvac control. The hissing could be that emission control thingy that goes to your manifold, it is right up against your firewall. I can't remember the name of the thing, but if you hear it, it is normally a ticking or clicking sound, not a hiss.

 

It's a hiss, and I've had a hell of a time trying to find where the lines go. I was sort of hoping the hiss from that device and the controls were related so I would know what to replace without having to rip the dash apart.

Anyone know what the proper name of that thing is so I can order another one?

 

I didn't say it was broken, no need to spend money so fast. Use a piece of hose to your ear to find the vacuum leak, just don't get it sucked into a moving part. you could have an exhaust leak in your manifold causing the sound too.

 

Vapor canister purge valve. Just found it on rockauto.com. Thanks for the emissions tip.