Air Conditioner Basics Part II - Thermodynamics

An air conditioning system uses principles of thermodynamics to cool a living space. In simple terms, it is a closed system that circulates a substance called a refrigerant, altering the pressure of the refrigerant at different points to promote the transfer of heat.

The Air Conditioning Cycle

We will describe the cycle starting indoors, where the refrigerant is a cold, low-pressure mixture of liquid and vapor that enters the evaporator. The indoor fan blows hot air from the living space over the evaporator, which absorbs the heat, cooling the air blown back into the living space. The heat absorbed by the evaporator turns the refrigerant completely into vapor, and is carried outside as the refrigerant travels to the compressor.

The compressor dramatically increases the pressure and the temperature of the vaporized refrigerant and drives it to the condenser. The refrigerant is now hotter than the outside air, and as that air is blown by the outdoor fan over the condenser, the refrigerant cools and condenses into liquid form.

The liquefied refrigerant enters the metering device, which lowers the pressure and the temperature of the refrigerant and sends it back to the evaporator, as the cycle is repeated.