Hi Roger,

The compressor is loaded and unloaded by the unloader valve. (see http://www.air-compressor-guide.com/air-compressor-unloader-inlet-valve.html)

The unloader valve is actuated by a small solenoid valve. The solenoid valve supllies and removed control air (compressed air) to the unloader valve, to let it open and close.

The solenoid valve is controlled from the main controller and connected by an electrical wire.

So, your problem could be in any one of those components.

I suspect it is the solenoid valve, as I have seen similar behavior like you describe before.

But, it could also be a loose electrical contact, or a loose (relay) contact inside the controller.

I would start with checking the solenoid valve. It is built up of two parts: the valve body and an electrical coil. The coil creates a magnetic field, which pulls the valve open.

You can try to clean the valve, or replace it with a new one. And you can try to replace the coil with a new one.

Good luck. And if you have any more questions, just let me know.