<P> Home freezers as separate compartments (larger than necessary just for ice cubes), or as separate units, were introduced in the United States in 1940 . Frozen foods, previously a luxury item, became commonplace . </P> <P> Freezer units are used in households and in industry and commerce . Food stored at or below − 18 ° C (0 ° F) is safe indefinitely . Most household freezers maintain temperatures from − 23 to − 18 ° C (− 9 to 0 ° F), although some freezer - only units can achieve − 34 ° C (− 29 ° F) and lower . Refrigerators generally do not achieve lower than − 23 ° C (− 9 ° F), since the same coolant loop serves both compartments: Lowering the freezer compartment temperature excessively causes difficulties in maintaining above - freezing temperature in the refrigerator compartment . Domestic freezers can be included as a separate compartment in a refrigerator, or can be a separate appliance . Domestic freezers are generally upright units resembling refrigerators or chests (upright units laid on their backs). Many modern upright freezers come with an ice dispenser built into their door . Some upscale models include thermostat displays and controls, and sometimes flatscreen televisions as well . </P> <P> Commercial refrigerator and freezer units, which go by many other names, were in use for almost 40 years prior to the common home models . They used gas systems such as ammonia (R - 717) or sulfur dioxide (R - 764), which occasionally leaked, making them unsafe for home use . Practical household refrigerators were introduced in 1915 and gained wider acceptance in the United States in the 1930s as prices fell and non-toxic, non-flammable synthetic refrigerants such as Freon - 12 (R - 12) were introduced . However, R - 12 damaged the ozone layer, causing governments to issue a ban on its use in new refrigerators and air - conditioning systems in 1994 . The less harmful replacement for R - 12, R - 134a (tetrafluoroethane), has been in common use since 1990, but R - 12 is still found in many old systems today . </P> <P> A common commercial refrigerator is the glass fronted beverage cooler . These type of appliances are typically designed for specific re-load conditions meaning that they generally have a larger cooling system . This ensures that they are able to cope with a large throughput of drinks and frequent door opening . As a result, it is common for these types of commercial refrigerators to have energy consumption of> 4 kWh / day . </P>

What kind of freon is in a refrigerator