Obviously it is a refrigeration compressor, the flanged connections give it away, it would also have a mechanical seal at the pulley end of the crankshaft. For purposes of air compression these are not generally a good item, as they are not designed to keep oil from being discharged with the gas; in a refrigeration system, oil routinely circulates through the system along with the refrigerant in its fluid/gas states; being that these are sealed systems, it is of little importance to keep oil from circulating the system, at least in small amounts.