The SFRD used heaters on produce movements when the trains went through the mountains so the produce would not freeze. Then re-ice in Albuquerque. This was seasonal.
In CA, they would pre cool the refers then add the produce and ice that was required. Citrus just filled the ends. Lettuce also added blown ice over the tops of the crates. In San Berdo, they would check the cars and based on the current weather, would add the heaters to keep the produce from freezing. Then at Albuquerque they would check and change again, then again in KC. The next stop was Chicago. Here the trains were split up for futher travel and icing or unloaded for market. Meat shipments usually added salt on the ice at every stop.
Phil