[Richard]

Air flows from the engine compressor to the Wet Tank. We know that is working because your supply pressure comes up. The air then flows to the brake tanks via the PPV. You have replaced it so you know where it is.

A small guy like me can crawl between the tags and access under the coach area.

I am very curious about something. When you tried the reboot of the air system by letting all the pressure out, did you pump the brakes and bring the secondary tank to zero? If so, did it rebuild to 120?

To the best of my knowledge there is only one PPV. So if the secondary tank built back to 120 after releasing then the PPV is working. There may be a check valve between the PPV and the brake tank. That is a big maybe.

How are your brake tanks drained? Auto, toggle pull, valved to exterior.? When you hook the coach to shop air, can you hear air escaping?

You have used the word the primary tanks builds lazily? Can you clarify? I was under the impression that it wouldn’t build any pressure. But if it builds any pressure, it is not likely the PPV. If it builds pressure, does it lose the pressure when you stop the engine?

Sorry for all the questions, I am trying to noodle out the diagnostic in public.