On a hot summer day, with the temperature soaring to new heights of discomfort, some folks will retreat indoors where the temperature is friendlier. Thanks in no small part to the efforts of an air conditioning unit. But how does this technological marvel work? You probably don’t have the slightest idea and that’s totally forgivable. After all, many of us haven’t the slightest clue either. But you’re here now and you’re reading this, so that must mean that you’re at least a bit curious. Well, an air conditioner works on the basic principles of heat transfer and changes in physical states.

Within an air conditioner is a liquid called a refrigerant. And yes, they’re found in refrigerators too because both refrigerators and air conditioners operate in much the same way with similar effects. The refrigerant being the substance that facilitates heat transfer, both systems rely heavily on its properties to cool the air. But first, hot air from the inside of your home is pulled into the air conditioner through a grille at the base of the machine. From there it is channeled through a system of ducts to metal coils called evaporator coils in which the liquid refrigerant is found. A fan blows the air over these coils and upon contact, the heat is transferred from the warm air to the liquid refrigerant, which changes to a gas. The air, now much cooler, is pushed out the air conditioner through another grille into your home.

But for this process to continue and the desired temperature to be met, the refrigerant must be changed back to a liquid. This feat is accomplished by a compressor, condenser coils, and a fan, which are usually located in a connected unit on the outside of a building. The gaseous refrigerant is sent to the compressor, which subjects it to high pressure. In doing so heat is generated in the process. But fear not, this heat isn’t channeled back into your home. That would be redundant. The pressurized hot gas is sent to the condenser coils. There a fan wafts air over the coil. Heat is transferred from the gas through the coils to the circulating air and the gas changes to a liquid. The hot air is released into the surroundings but the liquid refrigerant makes a return trip to the evaporator coil where the process begins anew.

Now I know you’re probably wondering, how does the air conditioner know when the air has reached the right temperature? Well, that my friend is the job of the thermostat. The thermostat monitors the air in the room and when it senses that the inputted temperature and the air temperature is one in the same it turns the air conditioner off. When the temperature in the room rises and deviates from the desired temperature the thermostat turns the air conditioner on, and the air begins to cool once more. But wait, there’s more. Some air conditioners called HVACs (heating and ventilation air conditioning units) possess an additional component called a heating element. The cooled air passes over this before being expelled out of the air conditioner. On exceptionally warm days this component is turned down, so the air that’s released by the air conditioner is cool. However, during the cold winter months, the heating element can be turned right up, heating the air before it leaves the air conditioner and raising the temperature inside your home. And that, quite simply, is how an air conditioner works.