So I'm new to this group. I have a bmy 5 ton 6x6. My air built to 120 n then I heard a click behind the dash and then it wouldn't build air pressure anymore and air was leaking out of the air dryer. When it first did it I was driving n pulled over n heard the air coming out of the dryer so I rebuilt that thinking it was the problem. Put it back it, built air great, hit 120 n then that was it, pump breaks to drain the air and it won't build up again.