Coolant, often referred to as refrigerant, is an important chemical compound used in air conditioning systems to remove heat from cars or indoor spaces and return cool air. There are a number of refrigerants out there, but the one most people are familiar with is Freon, or R22. However, while still in some older AC units, Freon refrigerant is being phased out due to its ozone layer-depleting properties and is being replaced with more eco-friendly refrigerants like Puron ( R410A) and even carbon dioxide.