The refrigerant is the key working fluid in an air conditioning (AC) system. It plays the central role in absorbing and releasing heat, which enables the AC unit to cool indoor spaces. The refrigerant goes through a cycle of evaporation and condensation, shifting between gas and liquid states as it moves through the system.

Inside the evaporator coil, located indoors, the refrigerant is in a low-pressure liquid form. As warm air from the room passes over the coil, the refrigerant absorbs this heat and evaporates into a gas. This phase change (from liquid to gas) draws heat from the air, cooling it in the process. A fan then blows the cooled air back into the room.

The refrigerant gas travels to the compressor, which increases its pressure and temperature. This hot, high-pressure gas then flows into the condenser coil outside the building. In the condenser, the refrigerant releases the absorbed heat to the outside air and condenses back into a liquid.

The cooled, high-pressure liquid then passes through an expansion valve, which reduces its pressure and temperature. This prepares the refrigerant to re-enter the evaporator coil and begin the cycle again.

Refrigerants are chosen for their ability to absorb and release heat efficiently. Older systems used refrigerants like R-22, which were effective but harmful to the ozone layer. Today, more environmentally friendly refrigerants like R-410A are common.

In summary, the refrigerant is the heat carrier in an AC system. Its unique ability to change states and absorb or release heat allows the AC to remove heat from indoor air and maintain a comfortable temperature.