AC Retrofit not working

My buddy is trying to get his AC working but he hit a roadblock trying to get the BMW's climate controls to trigger the 1JZ compressor. Everything works fine and blow ice cold when you trigger the compressor manually but we can't get the car's climate controls to do it for us, to turn it on and off. Just wondering what we're missing or what the BMW is looking for before it can trigger the compressor. All of the original parts are in place except for the Toyota compressor.