Thanks Richard,

I asked my friend who has a 1998 e320 to stop by. We exchanged the AC controls for the test and the failure is apparently with my unit, meaning it has also same behavior on his car and his unit works fine on my car.

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1996 E320 since 1/16/08, 171K miles as of Feb 2011

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1989 300CE - R.I.P. Dec 29 2007
Other MBs (sold): 1992 300E-24 - 1979 350SLC - 1984 230E - 1990 300CE