Installing AC in a 1980 928 without AC

[paris]

Hello everyone, I am trying to decide to install AC in my 1980 928 has no air, It is a Euro car. Does anyone know if the cars that were made without air have all the wiring there for AC? Does a 1980 need the AC button like the early car's or is it contained in the climate control unit, when you put the slider button in the blue does it activate the clutch on the compressor to come on automatically? What kinda problems will I run into? Any help on this project would be great. Thanks, Steve