2007 VOLVO 670 Air Compressor Issue

Please Helppp!!! I have a 2007 Volvo 670 with an Volvo D12 engine in it. I have a big issue with my air pressure, my air compressor is constantly running, building air up and it purges air every 30-45 seconds. I have so far replaced my air dryer filter (once in June of this year) and I am replacing it now again because it combusted (has two straight lines through the middle like someone cut it with a knife). I have replaced my shut off valve on the air dryer, and the rubber little gaskets that go in the valve. I have also replaced my firewall wiring that is under the hood on the side where the steering wheel is. Recently i replaced the fitting on the compressor that goes from the compressor into the little blue line, and I have replaced the air governor also. None of these things that I have done made the compressor stop building air, nor made it stop purgeing the air every 30-45 seconds.
Also on a side note since I replaced my air governor my PSI in my air tanks went down from 120 in the tanks to 100 before it purges. Please help I am sick of trying to figure out what is wrong with this darn thing

 

shoot beats me, its whatever they put in the truck when they built the darn thing. Not really sure how I can find out what kind it is? It's an Volvo Ved-12 engine if that helps any. The ugly green one. How dangerous is it to operate the truck with the air compressor constantly running like that?

 

I have had air leaks on the darn thing since I bought it. I have sealed of most of them the only other one that i have and is getting fixed tomorrow is a air leak inside the cabin under the steeringwheel (they call it the airwall or firewall something like that?) I had the console changed and it does not leak outside but it leaks inside the cab. The purge valve I have changed in June of this year. Is changing those unloader valves a major job? What do you suggest I should do, I will have a mechanic stop my air leaks tomorrow and if it keeps running what is my next step to do?

 

10-4 will do. I will have to call Gateway Volvo tomorrow and go get that kit. I would get it at fleet pride down on Hall St but that is where I got my new Air Governer and for some odd reason, since I put on that new Air Governer it only builds 100 PSI's into my air tanks, where as to my old one was building 120. Can Air Governors be adjusted? I heard some people said you can turn the screws on them and adjust how much they will build in the air tanks?

 

Thank you so very much, at least now I got a few things I can go by, I was worried that I will have to replace the whole darn compressor. One more question about the unloader valves, are they accessible, or is that a part that is IN the compressor?