Refrigerators require a coolant to work properly. This coolant chemical circulates continuously and rarely needs to be replaced because it does not get used up as the refrigerator operates. There are two main types of coolants used in refrigerators.
Freon used to be the most common type of coolant used in refrigerators. Most older refrigerators still use Freon its use has been banned in many countries. Freon gas is an optimal refrigerator coolant as it absorbs heat.
The major issue with Freon as a coolant is that is is considered a chlorofluorocarbon (CFC). These chemicals are known to cause harm to the ozone layer, and appliances that contain CFCs must be disposed of properly as the CFC will leak out over time.
Hydrochlorofluorocarbon (HCFC), is a type of refrigerator coolant used in newer refrigerator models. The types used today include HFC-134a, HCFC-142b and HCFC-22. HCFC does not harm the ozone layer.
A brine mixture of salt and water is used as a refrigerant in some areas where there is no electricity to keep food cool. As the water evaporates from the salt the mixture absorbs heat like any other coolant would.