2005 Mercedes Benz SLK350

Air Conditioning problem
2005 Mercedes Benz SLK350 Two Wheel Drive Automatic 25600 miles

the temperature drops after a few minutes - if I turn it off and back on it is cold again.
my mechanic says when I hit the button to that the red light indicator means the unit is off - every other car (including my 300 series mercedes) has the red light indicator as being the ON signal.
this does not make sense to me - can you tell me if he is correct?
either way I have a problem but still would need to know if he knows what he is talking about.
thanks very much.
June 9, 2009.

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