Chek the dimmer switch on the back side of the inst. cluster, they are known to fail. On the door panel the little black piece inside of the release handle comes out and there is a bolt or two behind it..there are also big phillips bolts under the door pull arm. then pop off all the plastic rivets on the panel and lift up.
As for the Air Cond. Have it checked by a pro!!

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM