Could anyone tell me the difference between the Harrison R4 switch and non-switch type compressor? The reason I ask is because I have a 1980 El Camino with a Chevy 350 which I put in from a Blazer, and it has a Harrison R4 compressor. The comprssor needs to be replaced, but I don't know if it is a switch or non-switch type. Any help is greatly appreciated.

Steve C.