The first set of R33 cars was placed in service on the train on November 15, 1962. Five hundred cars were built and served on all IRT subway lines. In 1972, they became the first A Division cars to be retrofitted with air conditioning when cars 9086/7, 9118/9, 9162/3, 9226/7, 9282/3, & 9294/5 were retrofitted at the 239th Street Yard with a modified version of the Stone Safety Air conditioning unit designed to fit on the smaller IRT cars, and by 1982, all R33 cars had received air conditioning. The cars were also rebuilt between 1987 and 1991.