Inlet and outlet on an early York should have shut off valves ( Roto locks. Service valves) for hi and low side on top of the compressor....
After you close off the system from the compressor you can slowly release the oil filler plug and let out small amount of freon from crank case.....add your oil and close it up...( total oil fill 6 to 10 oz depending on model .).open roto valves again....the oil level depends on the compressor fitted.
The single cylinder York is what it looks like....a twin cylinder looks like a little vee twin. (w/RV2.) at least, that's what it looks like.
I had a vee type on my old 1986 Dodge b200 van. Used up huge amounts of power. !
Found this.........
http://www.heco.net/Compressors.pdf
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