What type of freon is used in residential air conditioning units?

Residential air conditioning units primarily use R-410A refrigerant, which is a hydrofluorocarbon (HFC) blend. R-410A is preferred due to its efficiency and lower environmental impact compared to older refrigerants like R-22, which is being phased out due to its ozone-depleting properties. Some older systems may still use R-22, but new installations typically use R-410A.