Copper is superior than PVC pipes in many aspects -
Corrosion resistance - Copper offers a lot of resistance to corrosion, thus helping in preventing leakage of expensive refrigerant.
Weldability - Copper can be easily joined with the help of soldering at low temperature making leak proof joints. No need of high temperature welding and brazing.
Leaching - Copper at its purest form doesn't leach particles on the stream of flowing fluid, thus preventing choking of small passages in the coils.
Ductlity - Copper can be easily bended for a desired shape without much effort.
Crimping - Copper can be easily crimped for making end connections.