An AC refrigerant is a substance used in air conditioners that helps to cool the air. The most common type of AC refrigerant is Freon, which is a chlorofluorocarbon (CFC). CFCs are harmful to the environment because they deplete the ozone layer. As a result, the use of Freon has been phased out in many countries. Other types of AC refrigerants include hydrofluorocarbons (HFCs), which are not as harmful to the environment but are more expensive than CFCs.