Air dryer was leaking air out of the bottom port after air reached cut out pressure and it purged normally. Changed air dryer thinking the purge valve was the problem (cost the same as the valve alone). Didn't work, same leak after new dryer. I then discovered built up pressure in the small purge line coming from the governor (this is where the leaking air in the dryer was coming from). Took the governor off and found someone put a plug in between the air compressor and the purge port on the governor (where the gasket between governor and compressor is). I removed the plug and installed the governor correctly. But now the system does not purge at all! Pressure rises normally and seems to cut out at 125-130 psi but no purging. Could it be the unloader valve in compressor? What do you guys think?
Detroit 60 engine