xj heater

ok i have a 1991 xj the heater works but will only come out on the defrost no matter what setting you put it on it just comes out as defrost

Not sure about XJ's (I've only had mine less than a week) but on most cars the vents are controlled with vacum. There should be a vac. resovoir that may have become disconnected. You may also have a problem with any of the vac. lines, they get brittle with time. I believe the resovoir on the XJ is behind the front bumper. I know loss of vac. to the controls is a problem with Astros.
If I'm offbase concering XJ's I appologize in advance.

highilleer is right on the mark. The heater controls are vacuum actuated, and when vacuum fails the default setting is defrost. The vacuum reservoir is located on the passenger side behind the bumper. The most frequent cause of this problem is battery acid eating the vacuum hoses where they pass beneath the battery tray. Check that first.

Does you blower motor work? Mine was locked up and the only place I could get any flow was out the defroster when moving down the road. It could be your vacuum controls still work there just isn't any flow to redirect and the hot air is rising via convection and flowing out the defroster vents.

- JP