Air compressor acting weird

Hi Simon, if you replaced the governor, I'll bet it's the air dryer. Really not much else to it. Is the purge valve frozen? I've seen that too.

 

It is because you got an air leak somewhere in your wet tank or between a wet tank and a governor. A wet tank does not have a gauge connected to it to monitor air pressure.. You need to connect your own gauge to the wet tank to check for air leak. Mine acted like yours turned out to be a leaking unloader gasket (on top of compressor)
Here is a troubleshooting for AD-9 dryer: https://www.dropbox.com/s/1t78fzfv9is4qkj/AD-9 AirDryer Troubleshooting.pdf?dl=0

 

It could be something simple like a cracked hose from a wet tank to a governor. Spray some soapy water on it and watch for bubbles.. May not be easy on a Volvo with all fairings on place....

 

Run it up to pressure, pump the brakes to get the pressure back to the cut-in, and shut down once it starts building again, before it hits the cut-out. Listen for the hiss. If you have someone to help that's even better, or if you can hook up shop air to the compressor discharge line so you can pressurize without the engine running.

 

http://www.manualslib.com/manual/392698/Bendix-Ss-1-Shut-Off-Valve.html

 

Did you find what the problem is?