I have a 98 XJ and when i put the jeep under a load, like pulling a trailer or passing gear kicks in the A/C stops blowing out of the front vents and transfers to the defrost or the floor. anyone have any idea why this would be happening? seems to be getting worse over the years.

 

Look for any leak on the vacuum system for the heater controls,switch could be faulty,surge tank may have a leak or check valve is bad. When you accelerate your engine vacuum will drop from about 14" to 0-5" of vacuum,any leak or problem with system will be more noticeable.

 

99 XJ had the same problem. Replaced AC compressor clutch, that worked in my case.

 

Bigger/newer vacuum reservoir in the front of your bumer.

 

Yes sounds like you have a vaccum leak going to the vaccum resevoir.

The engine makes vaccum under normal conditions but under load/full acceleration the amount of vaccum is reduced, the vaccum resevoir(black ball thing) stores vaccum to use in that situation to make hope for low vaccum from engine.

Follow the vaccum lines going to the resevoir and listen for a hiss sound while running, also listen for a hissing sound in the dash also vaccum lines can also be loose there.