Hey, I have a 1999 Tj 4L sport and I'm having some issues with air flow out of my vents. Right now on any setting I'm only getting heat/air flow out of my windshield vent and very to no flow out of my 4 dash vents, and none out of my floor vents. I've checked all of the vac hoses under the hood and they all seem fine....kinda stumped.....NEED heat from the floor vents living in Thunder Bay, Ont....

 

Had some trouble like that with my car it was the cable in dash. The cable controled what vent the air comes out of. the cable came undone from clip that holds it in place. Hope that gives you some idea?

 

I had much the same problem 97 TJ, I removed the facia around the radio, requires taking out a feww screws, and found that a wedge of foam from the heater diffuser door had slipped out of place, and was blocking the door from moving.

 

hey Uhm I just had a heater problem with my 97 TJ. I had air only flowing out of "High" and nothing else. It turns out it was my Heater resistor. I bought a used one for 10$ and all it took was unbolting 2 bolts. It was located under passenger dashboard. I know this doesnt solve your problem but it could give you an idea on where to look? Only other parts I know are your heater motor or heater switch could be gone? But.. I cant give you any concrete answer. Just tryin' to give you more information. Cheers.

 

Had much the same problem with my 2000, changed the resistor and it worked for awhile. pulled apart dash and checked the back of the switches, sure enough the back was melted, I assume this is from the fan motor getting worn out. more resistance = more heat but I'm not 100% on that. anyways, I went to the scrapyard and 5 dollars later and another resistor and I can drive in the winter again.
p.s. other forums I have read tell me this is a common problem, at least with 00's and JP magazine has published a fix. I have not been able to find it though. Hope this helps.

 

It sounds like a vacuum line has fallen off somewhere. It defaults the blend door to defrost mode for safety reasons. Good Luck.

 

i agree with the vacume leak, also your jeep would be idleing a bit high.
it's proabaly the little L shaped hose that if looking at the engine from the front it attaches to the right side of the engine back near the brake booster but to the left on the engine, you should be able to see it just hanging there, real easy to fix just plug it back on the nipple you'll see sticking out of the engine i used a quick tie on it seems to work.
or there is a break in the line going over to under the battery where there is another plug the could have fallen off, just fallow the line from the first location i described to find the one under the battery.