I think you need everything. The entire AC system is gone. If I were you I would not worry about it. If you fix it, it will just brake down and need replacing in a few years or less anyway. Plus you gain a few extra horsepower by not having it. You would need the compressor, all the lines, the evaporator and everything else associated with it. The person who owned it before you probably took it out because all of them needed replacing anyway. You really can't fix AC parts, only replace them and once one part needs replacing, really it all will need replacing soon after. Am I right guys?