I would think there is a vacuum leak somewhere. Its not the booster since it works fine without the ac. Its it only at an idle? Does the idle boost come on?TheEmrys said:I just had an odd little problem. With the A/C on, I lose a good portion of my brakes. It seems like I either have a problem with my A/C or my brakes. My first thought is my brake vacuum booster is having issues keeping up with the amount of vacuum needed when the A/C is running. Anyone else have any thoughts? I'm ready to hit the auto-parts store and replace it, but if anyone else has had any other ideas, I'd like to hear them.