HCFCs (hydrochlorofluorocarbons), HFCs (hydrofluorocarbons), and natural refrigerants are classes of substances used as refrigerants in HVAC systems. HCFCs, such as R-22, are ozone-depleting substances (ODS) and contribute to climate change. HFCs, like R-410A, do not harm the ozone layer but have high global warming potential (GWP). Natural refrigerants, including carbon dioxide, ammonia, and hydrocarbons, have negligible impact on ozone depletion and GWP. The choice of refrigerant depends on the application, equipment design, and environmental considerations.