Here's the situation: my son was driving my 86 735i last weekend and heard what he first thought was static on the radio. He turned the radio off, but could still hear the noise, coming from under the hood. He shut off the car and could still hear a hissing sound coming from the front of the car. The AC completely leaked down its freon over a period of 1-2 minutes. He couldn't see or tell where the huge leak was. My question is: is there a high pressure safety valve somewhere in the high side of this system. I had a similar problem on a VW a few years ago where the high pressure thing blew leaking all the freon. I guess my only option is to partially charge the system and try to figure out where the leak is, unless any of you have a suggestion where to look first

Thanks in advance

Ben Charvet.