1991 Plymouth Voyager Air conditioning compressor stuck in

The air conditioning has failed in this vehicle long ago. However, after sitting a year we have decided to use the vehicle again. However, the air conditioning compressor appears to be perpetually stuck in the engaged position.

We would be happy to have it simply disengage as it if affecting the gas mileage and is making a terrible noise.

Is there a way to manually disengage the compressor clutch? Perhaps it has rusted in place?

Note: it makes no difference when we turn the unit on or off using the interior controls.