98 xj. Heaters stuck on defrost, cruise works perfect. Any ideas

 

Vacuum ball under front bumper. Or a vacuum leak in the lines.

 

There could be something wrong with the door that redirects the air, however the most common issue is the vacuum leak. The leak could be far enough up in the line to only cause issue with the vents, and maybe not so much with the cruise.

 

Where do.the lines start andbrun to where

 

There is a vacuum ball under the passengers side of the bumper. Disconnect and blow into the end with the fitting. If you hear a hiss then its the ball, if not, trace that now disconnected vacuum line up the fender and into the firewall. You should notice where the crack/break is.

 

when you find that ball in the front bumper and when you disconnect it, if you hear air gettng sucked into the ball then you know its not a vacume leek.

 

ok i checked the lines and where there is a T fitting up by the fire wall there is a screw stuck into the end. i looked at my buddies jeep and his has a line running off of the end of the tee where the screw is going into his firewall. its a very small vaccuum line. where does this line go into the cab?

 

That sounds like the line to the heater vents.. if you have a hand vacuum pump you could apply vacuum there and see if your vents work normally. If not, check the lines behind the heater controls. They can wear out, wiggle loose or just crack.