I have noticed that on my W140(300SD) two things about the AC..1)it does not seem to blow at a high max speed.....2)When accelerating with the AC I sometimes hear a whistling sound coming from the ducts...the air blows very cold and does not change volume when the whistling occurs...buts its an annoying sound.My 1992 300D 2.5(124) never had this whistling problem and also blew at a higher max fan speed. Took it to the dealer once for this at the last oil change and they said it didn't seem to be blowing quite fast enough but didn't really see any problem...any ideas?