i would blow the lines out with compressed air and some Dura 141, but that shit aint cheap. replace the exp. valve, drier, and any o ring you can get to. with a used compressor, i would probably not be too worried about installing it dry, but for safety i would throw in about 2-3 oz in it and 2-3 oz in the drier. pull a vac. for a few hours (or down to about 800 microns) and then charge and performance test.