Understanding the 4 Main Parts of an Air Conditioner

An air conditioner is a complex system made up of many components, but the four main parts that do the heavy lifting of moving air indoors and outdoors are the evaporator, condenser, expansion valve, and compressor. It's important to note that each of these components is located either on the outside (the hot side) or inside (the cold side) of the air conditioner.


The evaporator is situated on the cold side of the air conditioner. Its primary purpose is to receive liquid refrigerant and convert it into gas, which then cools and dehumidifies the air.

The gas absorbs all the heat from the air and carries it to the condenser.


The condenser is the counterpart to the evaporator and is located on the hot side of the air conditioner. Its job is to return that hot, condensed refrigerant gas to the outside to vent the heat and make the refrigerant liquid again.


The compressor is a large electric pump that works with the condenser to convert the refrigerant back into liquid. It does this by pressurizing the refrigerant gas. The compressor is also located on the hot side of the air conditioner with the condenser.

Expansion Valve

The expansion valve works with the evaporator, but is usually located between the evaporator and the condenser.

Its function is to regulate the amount of liquid refrigerant that enters the evaporator, where it is then converted to gas. Compression is an essential step in a refrigeration cycle, and a compressor is a device that increases pressure of a working gas. The refrigerant enters into a compressor as a low-pressure, low-temperature gas, and exits as a high-pressure, high-temperature gas. These components come in several different designs. Popular configurations include fixed orifices, thermostatic expansion valves (TXV) or thermal expansion valves (pictured above), and more advanced electronic expansion valves (EEV). However, regardless of their configuration, their function remains unchanged: to cause a pressure drop after leaving the condenser.

This pressure drop will cause some of that refrigerant to boil quickly, creating a biphasic mixture. This rapid phase change is called flashing and helps prepare for what comes next: The evaporator. The evaporator is the second heat exchanger in a standard refrigeration circuit and, like its counterpart, it gets its name because of its basic function. It serves as the “commercial end” of the refrigeration cycle, since it does what we expect air conditioning to do: absorb heat. This occurs when refrigerant enters in liquid form at a low temperature and at low pressure, and a fan pushes air through its fins, cooling it by absorbing heat from its surroundings and passing it to the refrigerant. After doing so, it's returned to its starting point: The compressor.

And so, in a nutshell, this is how a cooling circuit works. If you have any questions about how an air conditioner works or its components and how they work together, don't hesitate to reach out for help. We've been helping customers get optimal performance from their air conditioning and refrigeration equipment for almost 100 years.