Thunderbird5

Got a 97 XJ. No air comes out of center vent (sounds stuck). Other vents such as defrost and floor work fine. Slight amount of air continuously comes out of driver floor vent. Vacuum problem and how would I diagnose this?

texmedic49

I wanna say that when the bypass door vacuum thingy gets jacked up, the default air path is to the defrost vent. I seem to recall reading something to this effect somewhere, but I don't recall where right now. I know this doesn't help, but it might give you a place to start, and a bump.

jeep3200

If you do not have a service manual with the vacuum charts look here for help.

http://www.jeep4x4center.com/knowled...ex.htm#service

There are several things to be done. First check that you do not have any vacuum leaks under the hood in the line from the intake to the ball in the bumper.

If you have access to a electric vacuum pump it can make this easier.

If that is all OK then you can start testing under the dash with a either the electric pump or a hand held. Harbor Freight has a couple that are reasonably priced. Having one does come in handy. It makes testing the one way vacuum valves under the hood real simple.

Pull the center of the dash and the glove box to give you access to the vacuum control switch and the vacuum connectors. With the service manual chart and the hand pump you can see if the motors are activating and if there is a leak somewhere. I did this and found an issue with one of the motors for the dash vent. Had to take the whole dash out to fix it. It was not as bad as it sounds following the service manual.

Jeepnick

sounds like my problem, I'll have to try it.

texmedic49

Might as well clean the evaporator too while you are in there...

Slick761

And try not to break the little lights.... pita.

Thunderbird5

Texmedic-Thanks for the post. I have been curious about that. Because back when the forward vent worked, periodically I would be driving along and all vents would divert to defrost, then sooner or later it would return to the setting. Hopefully this will also fix that.

Jeep3200-thanks for the awesome post. That was my issue I was looking at a lot of vacuum lines and had no clue on which one did what. Going to take it into the shop tomorrow so I will use this info quite a bit. Thanks again and will keep ya posted.

mmattern1985

Just fixed the same issue on mine. It was two small holes in a vacuum line. If you have a vacuum pump it is the easiest and most accurate way to find a leak. Other wise you just can basically visually check the lines. Start by pulling one line off the vacuum ball at a time and checking it with the pump. If it looses vacuum then follow that line and you will find the problem.