[Richard]

Tony,

Building on Steve Bare’s suggestion, it is logical that since the behavior follows the change in air dryer that the change is responsible. But, that may or may not be the case. Make yourself a leak down tester and plumb it just after the air dryer. That first step will allow you to isolate the air dryer install from the rest of the coach.

And what a way to get to know all the different plumbing fittings!