Hi

I've recently had the same problem, if you are lucky it's not an expensive fix.

In my case it was the "evaporator Temp Sensor", but you have to pull out some info from the climate control display.

Follow the links below:

http://www.benzworld.org/forums/forums/thread-view.asp?tid=1175387&posts=12&fid=17

http://www.peachparts.com/shopforum/showthread.php?threadid=86110&perpage=15&pagenumber=1

Morgan