On my '03 S500 I was getting a very loud noise from what I beieve was the fan. Regardless of how high or low the blower was, the fan seemed very loud. After fooling around with it by pressing a few buttons on the climate control, the noise went away, but now the button marked ACoff has the red light on and it wont go out...Any one have any idea what was the cause of the the fan noise? Any trick to getting the ACoff button to work? I'm assuming the two are linked. but not sure.

 

the A/C off light staying on means there is a problem in the system. I'd suggest taking it in and having someone look at it. Depending on the sound, it could need a new blower motor and regulator.