1999 XJ, AC has good charge, works great at first start.
My wife and I took a trip to Vegas last weekend, AC started out fine.
Over the course of about 2 hours, cold air stopped coming out of the dash vents. Turned the fan on high, but no change to the vents. This happened with the wife driving. Opened the glovebox and lowered it down. Did a visual, all it tact. Audible sound of fan running, and the air is going somewhere, but not into the cabin. Noticed a change with vacuum change, grades seemed to close the vents, dowhills seemed to open them. Later during the week, I looked under the hood, checked hoses, no burns, cracks or breaks, and pulls vacuum. Something is breaking down after a certain amount of time. Any ideas? Took it to my local shop, and of course, its intermitant.

 

is air coming out of defrost vents maybe sounds like check valve in vacuum storage ball is bad

 

I didnt check for that. The escapaing air sounds to be going to the passenger side of the vehicle.
Also one thing I forgot to mention, as the mph increases, so does an audible wind noise, also from the passenger side of the vehicle, Previous owner had the windshield replaced, so maybe there was a poor install?