Residential air-conditioning is the most influential innovation in American life in the last 75 years, according to a survey conducted in October by historians at The Henry Ford and America Online. Nearly 2.5 million votes were cast in the survey, which reported penicillin, the personal computer, global positioning satellites, cell phones, broadcast television and the Social Security Act as other top innovations. Voters chose from a list of 75 items created by The Henry Ford institution.