I would just change everything as long as you are replacing the compressor. I have a CFC cert but do not work on the equipment
enough to know about every configuration. Generally, small compressors already come pre-loaded with refrigerant. You may have to flush the existing piping, connect the new parts
, evacuate the piping, then open the valves from the compressor to allow gas to circulate. Not sure what unit you are talking about that is pre-charged? I did not think that the evap would be pre-charged.