A few weeks ago we had some freezing weather . I wrote about this bus having a bad air dryer . So I unhooked the line going to the tanks .Felt the out put port of air dryer and had air going thru it . So I hooked it back up and went to the wet tank and pulled that line and I had a good amount of air pressure going into that tank .So I thought leak . This bus is a RE 300 and has a tone of air lines . So I pressure rise the system with shop air . I put a fitting on the wet tank . I heard air hissing with the system at about 60 lbs . Traced it down to the exhaust port on governor .Now the first thing I did before all this is install a new governor .What am I missing here ? Could I have gotten a bad governor ? When there is no air pressure in system it will build to 30 lbs and even that is slow .
I would change the governor again just to be on the safe side. Maybe you could bypass the air dryer and see if that changes anything. You might be getting air out of the dryer, but it may not be enough. You may also have an unloader valve sticking in the compressor.