My wife reports a recent problem with the a/c in 1999 C230K - I will try to relay her description and hope it provides enough info for replies. When the a/c is on and the fan is blowing, an occasional "whistle" sound occurs as if a vent is partially closed or something is impeding air flow. Also, occasionally the fan blower will continue to operate at the same speed after the fan control has been turned up. The fan speed will then increase shortly therafter to the correct speed. Is this a problem with the the fan motor only, or more? Thanks for your advice before I take the car to my indie.