You can purchase the same model compressor from different manufacturers one compressor will come completely with no oil another manufacture will ship it only with assembly lube or the amount of oil just for that one component the compressor let’s pretend it needs only two or 3 ounces then another manufacture will ship you the exact same compressor with the complete system charge of oil let’s say 7 ounces for example. Now you can see where things can go really wrong and cause a burned-out compressor come back or poor cooling performance.