When you say it won't blow on 123 your talking about the blower/fan Not AC?
that could well be the blower resistor that gone defective take a look at mypage.61.htm
that will show you the item and how to replace it. MB will tell you the dash has to come out , well thats rubbish, just a case of pulling the carpet back and using a mirror. Hope that helps
http://www.aclassinfo.co.uk/mypage.61.htm
