STALLING A LOT!

One of my employees drives a mid 90's xj 4.0(probably why he got hired, haha), but he is having troubles with it stalling on him a lot. He said he took it in to get checked out and they didn't fix the problem yet but it has something to do with it stalling when the defrost is on. I've never heard anything like that with an xj before, any ideas? Buz

my 91 used to do it, it turned out to be the body ground was loose

Battery could be shot too. (causing a huge load on the alternator, and thus the engine causing it to stall)