What substance is commonly used in vehicle air conditioning systems for cooling?

The substance commonly used in vehicle air conditioning systems for cooling is refrigerant. This term specifically refers to the fluid that circulates within the system to absorb heat from the cabin of the vehicle and release it outside, thereby providing a cooling effect.

Refrigerants are designed to change states from gas to liquid and back, allowing them to absorb significant amounts of heat during the evaporation process and release it during the condensation process. This cycle is fundamental to how air conditioning systems work, and the efficiency and effectiveness of a vehicle’s cooling system depend on the properties of the chosen refrigerant.

In contrast, coolant generally refers to fluids used to manage engine temperatures, antifreeze is a type of coolant specifically designed to prevent freezing in cold temperatures, and compressant isn't a standard term in this context; the correct term would be compressor, which is the component that compresses the refrigerant to initiate the cycle. Thus, refrigerant is the most accurate answer regarding what is utilized for cooling in vehicle air conditioning systems.