I have just done this, I am very lucky to have a friend who is very good with VAG cars and vans who helped me. I took the full air con system from a donor van. The front end needs to be removed to run wires to under the battery and fit the condenser, pump etc. The dash needs to be removed to swap out the heater box and add in the additional wiring. Holes need to be made in the bulk head for the condensor pipes and drain. It’s a big job and well worth it but as I say, I’m very lucky that I have a knowledgeable friend to help me.
The hardest part is the wiring so if you have access to wiring diagram then the rest is mechanical pretty much.