Volvo A3000 not building air pressure

[fmatemberere]

Please help, our Volvo A3000 Water Truck is not building air pressure and cannot engage gears or release the park brake. I disconnected the outlet line from the air compressor and started the engine and idle it.. The air compressor is pumping but not sure if the pressure is good enough because I could put my hand on the outlet tube without getting much resistance from the air pressure. How much pressure should I get from the air compressor at idling speed please.

Thank you

 

[BigWrench55]

It's been a while since I troubleshot a air system. I would start with the governor first and if that doesn't work then I would suspect the Reed valve on the compressor.