The C class cars got the "summer opening" or "rapid ventilation" feature starting in MY 1998. That's the year they switched from infra-red locking to radio frequency. The thinking was that with IR locking, the button may be inadvertantly pressed and held, opening the windows and sunroof accidentally. With radio frequency the button must be pressed, held, and AIMED at one of the receivers ( door handle(s) or trunk button ) from only a few feet away, eliminating the possibility of unintended opening.