Without getting too specific, it depends on the cars involved. Air conditioning began to be applied to diners and lounge cars in the early 1930s, some of which was ice and some with the various mechanical systems then available. All streamlined cars were delivered with mechanical A/C and some ice A/C cars were later converted to mechanical. Other ice cars, particularly some heavyweight coaches, remained ice A/C for their entire career, into the early 1960s.

If you need specific car information for 1943 and later, the T&P listings in the Official Register of Passenger Train Equipment (published once or twice a year) will usually list the type of air conditioning in each car, and you can fairly readily view the transition from that time forward. Pullman was also air conditioning their cars by the early 1930s, following the same general approach.

Bill Pollard