Evan Leisey wrote:

. . . other than the obvious labor intensity and icing delays of the iced cars, what are the pros and cons of the ice versus the mechanical cars. As I know only of flowers being shipped in iced reefers, assume that humidity was a concern.

The biggest factor keeping ice refrigeration in service was that ice provided a huge capacity to absorb heat in a fairly rapid fashion. That meant that produce could be loaded right into the reefers, uncooled, and still have a fast enough temperature fall in the early part of the journey to market, to travel properly. The early mechanical reefers had very limited ability to do this, as they only had a limited heat absorption capability in their air handling (they were designed, as I said, for frozen food, which was loaded at shipping temperature, thus the cooling system only had to deal with small amounts of heat entering the car surfaces, NOT with heat of the cargo itself). The large "heat of melting" of water ice is the key, a familiar fact to engineers and scientists.
When "wide range" mechanical reefers were first built at the end of the 1950s, the big change was vastly greater cooling capacity in the refrigeration systems, so that they could do the job of the ice cars.

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