I've replaced everything on cars from headlights to engines and transmissions, but one thing I will not do ever again is AC. It's too tricky.

The slightest bit of dirt in the system and the expansion valves malfunction. If the system is partially discharged I'd recharge the freon or puron, but once they are totally drained and have holes they get moisture and dirt in the system and pretty much need to be rebuilt. IMO when that happens spend the little bit extra I've found and take it to someone that specializes in it, or someone you are confident can rebuild a clean system.