Air Recirculation Mode
WARNING: This page is about a different car, the 1997 Mercedes-Benz C280 and 1997 Mercedes-Benz C230. However, it is still accessible from the selected car via links, so may be relevant.
Pressing air recirculation switch causes air to be recirculated without additional fresh air. Air recirculation mode switch automatically shuts off after specified period of time. Air recirculation mode cannot be turned on if defrost button is pressed.