96 b2500 van.... Am realizing from other posts as my clutch will not engage (stopped working after having new tranny fitted) that compressor can shut down from lack of oil , is this somthing i can check and fix...also is the square block connector that is inline on the wires from the top of the compessor also some type of fuse.

 

Lack of R-134a refrigerant, not oil will prevent the compressor from running. Lack of oil will destroy a compressor, much like running an engine without oil will.

As to the block thing on the compressor wiring harness, never seen it.

 

Thanks, will look to other reasons, tried adding r-134a with ac on cold and running but gauge immediately showed way in the red. should a lower pressure not show if all is correct..

 

Correct to a degree. Yes a lower pressure can read on the gage and still not activate the compressor. But since yours is in the red zone then your pressure appears to be fine, it will always read high when the system is not running. You will need to check that the wiring and AC relay are working. Most likely either the relay or circuit to it is bad or one of the sensors in the circuit are bad.