Here is a summary of Service Order 104 from  “Freight Car Distribution And Car Handling In The United States” by Eugene W. Coughlin (1956).

In essence this was not designed to put the reefers in a national pool per se.

Bob Chaparro

Moderator

Citrus Industry Modeling Group

https://groups.yahoo.com/neo/groups/citrusmodeling/info

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Several orders were issued permitting or requiring the substitution of not more than three refrigerator cars in lieu of one box car for loading to certain areas. The most extensive use of this type of order was Service Order No. 104, issued on January 19, 1943 , which was designed to reduce the excess movement of empty refrigerator cars to destinations in five western states by using them for freight usually loaded in box cars. With a tremendous flow of empty box cars eastbound from California and nearby States and a heavy westbound movement of empty refrigerator cars to that area, it was obvious that an order providing for the substitution of refrigerator cars for box cars on westbound traffic destined to that area would make a corresponding reduction in the cross-haul of empty refrigerators moving west and empty box cars moving in the opposite direction.

The original order provided that railroads, "transporting westbound trans-continental shipments, in carloads, destined to points in the States of California, Idaho, Arizona, Nevada and Utah might at their option, furnish and transport not more than three refrigerator cars of Pacific Fruit Express or Santa Fe Refrigerator Dispatch ownership in lieu of each box car ordered subject to the carload minimum weight which would have applied if the shipment had been loaded in a box car".

Service Order No. 104 specified that it did not apply to shipments on which the carload minimum weight varies with the size of the car and suspended all rules, regulations and tariff provisions that were inconsistent with the order. As originally issued the order was permissive as applied to carriers and mandatory as applied to shippers. Subsequent amendments to the order made changes in the territorial application and made it mandatory for carriers to supply refrigerator cars, "when freight to be transported is suitable and facilities are suitable for loading in refrigerator cars, and when PFE or SFRD refrigerator cars are reasonably available".

Commodities on which the carload minimum weight varied with the size of the car were also included by an amendment which directed the substitution of two refrigerator cars in lieu of one box car ordered of a length of forty feet, seven inches or less, and three refrigerator cars in lieu of one box car ordered of a length of over forty feet, seven inches, and not over fifty feet, seven inches, subject to the carload minimum weight which would have applied if the shipment had been loaded in a box car of the size ordered. This amendment also appointed as Agent of the Commission the Manager of the Refrigerator Car Section, Car Service Division, Association of American Railroads and authorized him to direct the use of refrigerator cars, other than PFE and SFRD cars, and of either private or railroad ownership, for loading as provided in the order, if PFE and SFRD cars were not reasonably available. Acting under this authority the agent of the Commission issued several permits to railroads authorizing loading of refrigerator cars of miscellaneous ownerships where sufficient PFE and SFRD cars were not available to meet requirements.

Service Order No. 104 made an important contribution toward more efficient utilization of both refrigerator and box cars by reducing the empty haul of both classes of equipment used in trans-continental traffic, despite the fact that refrigerator cars could not be used for any kind of freight that would damage the interior walls, insulation, floors, floor racks or bunkers of refrigerator cars, nor for freight requiring the use of dunnage or bracing that would damage the cars.

Additional disadvantages in the use of refrigerator cars for box car traffic resulted from the fact that the doors of the majority of refrigerator cars swing outward and at many industries where freight is ordinarily loaded in box cars, refrigerator car doors cannot be opened or closed while the cars are spotted at the loading platform.