Let’s start with getting some AC related vocabulary out of the way:

BTU: stands for British Thermal Unit and is a measurement of the amount of heat required to raise or lower the temperature of one pound of water one degree Fahrenheit. The higher the BTU, the faster it will cool a space, so ACs with higher BTUs are good for larger spaces or cooling multiple rooms.

Compressor: a pump that increases the pressure of refrigerant gas in a cooling system.

Condenser (outside) Coil: it removes heat from the refrigerant in warm seasons, allowing the refrigerant to be converted from vapor to liquid and complete the refrigeration/cooling process.

Condensing Unit: it moves energy in the form of heat by compressing a gas known as a “refrigerant,” then pumping it through a system of coils and using the air around the coils to heat and cool spaces.

Evaporator (inside) Coil: an AC component that absorbs heat in the air in order to change the liquid refrigerant that flows through it into a vapor initiating the cooling process.

Freon: a specific type of refrigerant that is most commonly used in air conditioners

Refrigerant: the specific type of chemical fluid used in ACs, refrigerators, and heat pumps to transfer heat into or out of an interior space.


To boil it down, an AC works in the following steps:


Step 1: Evaporator coil absorbs heat from the air

The warm air inside your house is transported to the cold evaporator coil. As the refrigerant absorbs the heat from the passing air, it changes from a liquid to a gas and continues to travel over to the compressor.

Step 2: Compressor raises the refrigerant temperature

The compressor decreases the gas’ volume, which raises the pressure and temperature of the refrigerant. It is now ready for the condensing process.

Step 3: Fans and ducts transfer the heat outside 

The refrigerant is now a superheated vapor and it reaches the condenser coil and is exposed to the outside air. The outside air absorbs the heat from the refrigerant, lowering the temperature of the refrigerant and changing the state from a gas back into a liquid.

Step 4: Refrigerant temperature drops; process repeats

Once the heat from the refrigerant is removed to the outdoors, the cold refrigerant travels back indoors to the evaporator to repeat the process over again. The process continues until the inside temperature of your home reaches your desired level. At this point, your thermostat tells your AC to shut off.