1999 Nissan Altima stalls at idle with ac on after it is driven for awhile

Try checking the throttle to make sure it's not too low. I had the same problem but my altima would turn off when I made a sharp turn. I suspect that when you turn the A/C on the air compressor drains so much of the engine's (pulley) power that it stalls. See if it helps to tighten that.

http://i56.photobucket.com/albums/g179/Marikawn/throttle.jpg

I'm no mechanic but I might as well be.