I am very interested in this cause I have a similar issue. Best I can describe is it is intermittent at best. Not a freon issue, not a compressor issue (It turns even when there is no cold air). I am suspecting the ac control panel or pressure sensor. It seems like when it is really hot and the car sits outside it just wont work. I did evacuate the system and clean out the compressor safety valve and filter, it was quite contaminated. So I also think I may have a condenser issue too.
2004 330i ZHP