York and Tecumpseh compressors haven't changed in the last 50 years except for the hose connections. Since they were piston type, they vibrated and broke mounting brackets and still did this until about 10 years ago when rotary compressors became standard in the trucking business. GM was way ahead of their time with the rotary compressors they used on passenger cars. I don't know what they used on trucks because no one around here could afford one.