Mercedes Aircon Recirculation Problem

I have a 1996 C180 with AirConditioning.
The problem is that the Recirculation Button. (This is when you shut off the fresh air) When the Switch is pressed, the red light stays on, but this doesnt shut off
the Vent . I am told that this is done through a Vaccuum process, and in fact the 'actuator' doesnt actually turn, when the button is pressed. The actuator is behind the passanger airbag, and can be reached by taking out the glovebox, and putting your hand through. However Merc have told me that to replace it would mean taking out the ENTIRE dashboard, which could cost 700 +. An Aircon specialist told me its a 12/13 pound part. I have no idea what to do.
Any ideas comments and or suggestions please ?
Thanks
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