How cold could early refrigerator-freezer combinations keep their freezer compartments?

Early home refrigerator-freezer combinations were designed to maintain freezer-compartment temperatures as cold as 15° F (-9° C). This temperature was sufficient to store quick-frozen foods for periods of weeks or months.1

While these combination units provided essential storage, the subsequent development of separate chest-type freezers allowed for even lower temperatures, often reaching 0° F (-18° C), which enabled the safe quick-freezing of fresh foods.1