[77newell]

A couple additional thoughts. The usual way to hook up the air system is to take the output of the air dryer and run a line to the front of the coach to the service tank and then lines from that tank to the other two tanks, one of which is right next to the service tank. If the factory hooked the tanks up wrong I think it likely that the line to the service tank got hooked to the front brake tank and then that tank's lines run to the service tank and the rear brake tank. In that case the problem exists somewhere between the front brake tank and the service tank, that is within a line about 2 feet long with a check valve in it. Other than the check valve the only way to stop the air flow would be if the line was choked off either by being kinked or by internally collapsing if it is a hose rather than tubing.