In 1954 NP bought 50 mech reefers mostly for frozen food service, and in 1956 MILW (URTX) bought 40 cars from PC&F. Both groups had electric heaters and could maintain -10 to 60 degree temperatures in any weather.
But as Tony noted unless the cargo is pre-cooled ice was still required. I saw a load of carrots being unloaded once (circa 1968) from a mech reefer and there was "top ice" (shaved ice) that had obviously been blown over the load through the doors. This also was a practice used in ice cooled reefers.
