drain all the oil out of the compressor and measure it. replace the orifice tube if it has one. If you see any metal in the lines or orifice tube then you'll need to flush the lines with a suitable solvent, don't flush stuff into the accumulater, remove accumulater and seal the ends off before flushing. Replace all seals with new ones for safe measure. Try not to blow moist compresser air through the lines. Add the correct weight a/c oil back to the compresser, same amount as you removed. I like to add one additional ounce. After reassembly its pretty much just pull a vacuum for 30 minutes, seal it off and recheck the vacuum level after 15 minutes to verify you don't have a leak. Next you're ready for the refridgerant.

I know we have a couple a/c techs here online, just don't know if they're around today.