Radio removal tool is available from the dealer for under $10. Or from Samstag Tools:
http://www.samstagsales.com/mercedes/mb_radiotool.jpg
In general to get to the AC pushbutton you would have to remove:
1. Ashtray wood cover
2. Plactic frame around shift lever
3. Wood cover from the shifter console (the one with the window switches)
Items 1 - 3 follow instructions from JimF page:
http://pages.prodigy.net/jforgione/BW_fgs.html
4. Remove radio (make sure you have a code)
5. Remove center console wood cover:
two small philips screws at the bottom in the ashtray area and two small phillips screws in the radio openning. Then lift cover at the bottom to horizontal position and pull it back to disconnect hooks at the top.
6. Remove AC control - two small phillips screws.

Good luck