'91 XJ Heat and air only coming through the defroster?
 

So today was a cold day in Colorado, the coldest in awhile, heat was needed in the Jeep after a few months. So driving around a bit I eventually noticed my face was pretty hot, but my feet were still freezing. So I reach down by the vent, nothing. But up on the defroster area its blasting out hot air (it was on "Heat" mode)...So I put it on defroster, to see if they would swap. Nope still all coming out of the defroster. I got to the point of trying all settings on all the vent selections, and found that no matter what I had it on, cold air, hot, air, vent etc. it was all coming out of the defroster; even when I had it in the "off" position, there was still a draft coming out of the defroster.

What in the world?

I am being told its possibly a switch on the heater hoses on the passenger side. I taped it the part that moves on the switch down, but nothing changed..?

Vacuum issue, all the vents are control by suction off the engines intake, including the one that seals the fresh air vent outside the cab. Try checking every inch of the tubes. One thing i noticed with my '92 is if i have the engine under a heavy load (Something as small as trying hold my speed in 5th gear) the vents switch to the defroster.

^^ This ^^
Also check the vacuum ball under the front passenger side bumper for cracks.

XX2 what they said.. w/o vacuum the vents 'default' to the defrost position. Probably just a loose vacuum hose somewhere. It could even be behind the controls themselves. The vacuum reservoir should be behind the front bumper on the pass. side if you need to check that.

Well I checked for loose cracked hoses, nothing. But while trying to get that vacuum odd ball shaped deal, I broke part of the line off no cracks on the vacuum ball; either way I just hooked the boot up to a piece of line in the engine bay on the passenger side and then plugged the vacuum thing in to test it out, still didn't work. Now I'm stumped, even plugged those black and white connectors backwards. But nope...anyone have a clear pic or diagram of how they should be set up, particularly on the pass. Side behind the fuse box?

How hard is it to get into the actual switch mechanism? And how do you mold it back on? Mine is melted on, of some sort...

Has no one removed the switch console? Cause I'm about to take that off and get into there but I don't want to break anything etc. And I'd like to be sure that's the problem if I have no cracked vacuum lines etc.

I have twice, but only a few inches to check the lights in it. I can only get it a few inches out before it fights me. So i would look up how to do it first lol.

Well yeah I just went ahead and got in there: I don't really know what too look for though and everything seems fine excluding the dead light bulb..I do know that none of my vaccum lines feel like the have suction. I'm not sure if u can tell by finger though...anyways I'm stumped. Everything i can see is fine, anything else I could check?

Check the lines again - symptoms point to vacuum line leak.

Solved: After installing a 99+ manifold and connecting my vacuum lines again I put the check valve to the heater hose on incorrectly...Yep took nearly 3 years for the idea to pop up in my head of simply swapping the valves direction...

I just want to commend you for coming back after three friggin' years and letting us know the solution. I have a vacuum leak somewhere between the firewall and the controls under the dash (I guess), because everything that functions with vacuum works except that I get a shift from the vents to the defrost when the engine is under load. Cruise control works fine. What I don't seem to see anywhere online is pictures of what to look for in the dash, or how to get there...although it seems like I did see something about getting in there through the glovebox. I'm going to mess around this weekend and see what I can get to, and hope it is pretty obvious.

Thanks again for coming back with the eventual solution.

On the cabin temperature control panel, once removed there are three connectors on the back. The left is the electrics plug and is usually melted to some degree. It controls the fan speed. The center connector is the vacuum connector. It controls, along with the vent selector on the front panel, where the air will be directed, floor, side vents, bi level and defrost. Check to make sure that is completely seated and check the hoses on the back. Make sure they are all there and have no breaks. The are made of a rubber material.