So i have Been searching for a couple days now on this subject, And just can't find the right answer..
I have a 1992 Jeep cherokee Laredo, the heat and air only come out of the defroster and floor not the vents, I checked the vacuum lines and they all are good and hooked up. Leads me to the acutal switch its self.. But im not sure..

 

Check for a vacuum leak, maybe in that little bubble thing behind the bumper on the passenger side.

 

I went and looked at it just about 30 minutes ago and as far as i can tell no holes or cracks.. But from what i read, theres more then one vacuum line going to it right? or just one.. Because i only see 1 line

 

No one else has any advice?

 

There are two hoses. One one each end. Mine did the same thing. One of the hoses was disconnected. That is the vacume canister. That's where I would start. Follow vacume lines. They could be cracked and leaking or disconnected.

 

Okay I see the one on the right side, I just got all my speakers so while I'm doing that ill take a look.. thank you

 

Well looks like all is good now.. just have to figure out why ac not blowing cold... Could be because my ac lines are all rusted.. thanks for the help