cuiseotrol need info

hi all,trying to diagnose the cruise on a 85 380sl.looking at the actuator in parts they call it a vacuum actuactor.that confuses me. it has no vacuum hoses going to it and it does have an electric motor on it. can any one explain this.....does the motor run an internal vacuum pump? is there a diaphragm inside or what?????? I have Mitchell on demand but can find no info on how the actuactor works. please help