Evan Leisey 4 wrote:

If within the discussion period of this list, when did mechanical reefers enter service? Assume since passenger cars began using mechanical air conditioning in the late 30's that reefers would have been soon to follow or did they precede passenger cars?

There were a variety of experimental mechanical reefers built as early as the 1920s, but none were successful on any scale until after WW II. The usual explanation is the robust GM small diesel engines, developed for various military applications, which were the first truly dependable power for onboard compressors to run refrigeration. The early mech reefers, until the late 1950s, were exclusively for frozen food and in fact did not have thermostats permitting temperature setting in the range used for fresh produce.

The discussion of roses being shipped via reefers prompted questions, 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.

Humidity was a secondary concern. A bigger one was air circulation to ensure uniform temperature. This was solved by design of air circulation paths entirely around as well as through the cargo compartment. In the early mechanical reefer days, top icing was practiced to provide desired humidity for some cargoes.

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