In addition to what has been pointed out, I also note that, at least in my 328i (F30), the fan is always in recirculation mode when the air is on. That is why some note the fan is so loud when it is turned up (with the AC on). The recirculation door is opened up under the passengers footwell. At first I thought mine was defective, but maybe it is by design to make the AC more effective. Put the fan in auto or outside air mode, turn the fan up some so you can hear it and push the AC button on/off. When you turn the AC on, you can hear the door open and the fan gets very loud (without any change in air volume coming out). This drives me crazy. I have to turn the fan to the lowest setting (in auto mode with AC on) to quiet the fan. I would be interested if others have noticed this. It may be something you don't realize unless you are aware of it.
Last edited by blonyskin; 09-04-2012 at 07:40 AM.