I've posted about this prob before, but I didn't ever seem to find a solution, and now its not just dealing with my heater.

My '91 XJ seems to not be able to open the vents. No matter if I put it on Heat or Vent, the air continues to only come up through the windshield. Now, it understands which type of air I want; if I put it on red (heat), I get hot air. Put it on blue (cold) I get cool air. I just can't get it to come through the vents. Please help, because my family and I are going on a trip this weekend, and this would be beneficial to use. Thanks guys!

 

Check the vacuum hoses to the heater control and down under the passengers side dash. There is also one that comes in on passengers side firewall, IIRC>

 

Check the vacuum ball behind the front bumper passenger side, the hose could be cracked. Mine did the same thing but I also lost the cruise control, checked the vacuum ball and hose and everything looked good, started checking around the intake and found a line off at the intake. Hope this helps.

Wahoo

 

^^^ This. Sounds like you have a vacuum leak.

 

Alright, so checking all of these lines is my first priority come morning... because right now its dark and I probably wouldn't fair well with looking for cracks lol.

Is there any fool proof way to check these lines? Like smoke, or something? Also, I think my vacuum ball was relocated. I have this ball looking thing right near my battery that has a line running to it that goes to the firewall.