Hello my name is Frank and I am here to assist you. The air is coming out of the exhaust port. When the valves are pulled out no air goes to the trailer supply line and no air goes to the park brake on the tractor. In this state the exhaust ports are open on both valves and any air feeding back from some where else will leak out the exhaust. To trouble shoot with the valves in the applied position ( buttons out) pull the delivery lines from each valve one at a time. There should be no air coming back . If it does it could be a bad two way check valve that controls primary and secondary air that supplies the valve or a bad tractor protection feeding back. Start with these checks and reply back to me if you need more assistance.
Thanks for your reply. So with both of the buttons out and system pressurized just pick one of the valves and remove the line attached to the delivery port of the valve? And if the first one I pick does not have any air coming out of the disconnected line then reconnect and check the next one to isolate the feed back? Am I checking for air coming from the line or the port where I removed the line from the valve?