<P> Many refrigerators made in the 1930s and 1940s were far more efficient than most that were made later . This is partly attributable to the addition of new features, such as auto - defrost, that reduced efficiency . Additionally, after World War 2, refrigerator style became more important than efficiency . This was especially true in the USA in the 1970s, when side - by - side models (known as American fridgefreezers outside of the US) with ice dispensers and water chillers became popular . However, the reduction in efficiency also arose partly from reduction in the amount of insulation to cut costs . </P> <P> Because of the introduction of new energy efficiency standards, refrigerators made today are much more efficient than those made in the 1930s; they consume the same amount of energy while being three times as large . </P> <P> The efficiency of older refrigerators can be improved by defrosting (if the unit is manual defrost) and cleaning them regularly, replacing old and worn door seals with new ones, adjusting the thermostat to accommodate the actual contents (a refrigerator needn't be colder than 4 ° C (39 ° F) to store drinks and non-perishable items) and also replacing insulation, where applicable . Some sites recommend you clean condenser coils every month or so on units with coils on the rear . It has been proven that this does very little for improving efficiency, however, the unit should be able to "breathe" with adequate spaces around the front, back, sides and above the unit . If the refrigerator uses a fan to keep the condenser cool, then this must be cleaned, at the very least, yearly . </P> <P> Frost - free refrigerators or freezers use electric fans to cool the appropriate compartment . This could be called a "fan forced" refrigerator, whereas manual defrost units rely on colder air lying at the bottom, versus the warm air at the top to achieve adequate cooling . The air is drawn in through an inlet duct and passed through the evaporator where it is cooled, the air is then circulated throughout the cabinet via a series of ducts and vents . Because the air passing the evaporator is supposedly warm and moist, frost begins to form on the evaporator (especially on a freezer's evaporator). In cheaper and / or older models, a defrost cycle is controlled via a mechanical timer . This timer is set to shut off the compressor and fan and energize a heating element located near or around the evaporator for about 15 to 30 minutes at every 6 to 12 hours . This melts any frost or ice build up and allows the refrigerator to work normally once more . It is believed that frost free units have a lower tolerance for frost, due to their air - conditioner like evaporator coils . Therefore, if a door is left open accidentally (especially the freezer), the defrost system may not remove all frost, in this case, the freezer (or refrigerator) must be defrosted . </P>

When was the first side by side refrigerator made