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How does air conditioning work? Basics

Residential air conditioning has become an essential appliance in our homes, especially at certain times of the year when the heat becomes intense. Furthermore, with reverse cycle air conditioning, you can adjust the temperature as you want.

But despite the essentiality of what air conditioners do, what we want to show you today is the technology behind air conditioners and how it works, as it may be less complex than you think. Understanding it will also help you deal with AC problems, understand breakdowns, and choose one model over another when acquiring your AC for the first time or changing it.

What does its operation consist of?

First of all, it must be said that a normal air conditioner works thanks to thermodynamics applied to the use of a particular type of gas with specific characteristics. The most widely used currently, because it is capable of guaranteeing great savings from the energy point of view, is R32 gas.

The operating mechanism of an air conditioner consists of a constant process of increasing and decreasing the temperature of this gas, through a compression and decompression system.

An air conditioner is made up of two parts. An external one, which is essentially the engine from which the process starts and which is installed outside the home and an interior one, commonly called “split”, is the part that ends the process, putting cold or hot air into the space where it is installed. The internal machine can be wall-mounted, portable, or channelled.

What are the parts of an air conditioning system?

Contrary to what many believe, air conditioners do not generate cold air and “expel” it, but rather extract the heat from the air in the room to be heated.

The operation of this basic refrigeration circuit where a refrigerant gas runs through a circuit of copper pipes changing from a gaseous to a liquid state and vice versa as it passes through the different components of the system.

The constant changing in the state of the refrigerant is what causes the thermal exchange that allows the air conditioner to extract the excess heat from the air and to condition the room.

air conditioning service maintenance


Indoor unit

Also known as split, this element is essential to understand how the air conditioning works. The indoor unit of the air conditioner, which is the one located inside the room to be cooled, contains an evaporator.

This part is responsible for extracting the hot air from the room and transferring this same heat to the refrigerant gas. Inside this unit, there is also a fan to distribute the air once cooled.

Outdoor unit

The outdoor unit is in charge of expelling the hot air from inside the room to the outside. It is made up of three parts: compressor, condenser and expansion valve. The compressor is the most important element in the refrigeration circuit, the one that consumes the most energy and the one that determines how the air conditioning works.

What the air conditioning compressor does is compress the gas that comes from the evaporator in a gaseous state until it becomes a liquid and heats it. The compressor works according to the speed set by the temperature sensor controlled with the thermostat.

For this reason, when the indicated or programmed temperature is reached, the compressor slows down, even turning off.

Refrigerant gas

The refrigerant gases change their state from liquid to gaseous, absorbing, in this process, the heat from the room.

Expansion valve

The expansion valve causes a loss of charge in the refrigerant and a drop in gas pressure and temperature. This process is similar to that used by sprays: inside there is a gas in a liquid state and when pressed it sprays and comes out cold.


The thermostat is an electronic component that is used to regulate the operation of the air conditioning. Optimal use of thermostats can help you save up to 30% on the energy consumption of your air conditioning.

What are the phases of air conditioning?

The refrigeration cycle is the set of processes by which the refrigerant gases pass from one state to another until they return to their initial condition. This cycle is made up of four phases or processes.

young women turn on air conditioning


Expansion phase

The expansion is the first phase in which the refrigerant is in a liquid state and at high pressure. Also, it is stored in the outdoor unit of the air conditioner. As it is necessary to send it to the indoor unit to achieve the cooling effect, this process is done through the expansion valve.

The purpose of the valve is to reduce the pressure and temperature of the liquid, leaving it in optimal conditions for the next phase.

Evaporation phase

Inside the indoor unit, there is an evaporator, which is what allows the liquid gas to evaporate. After this process, the liquid, already converted into gas, gives up its cold to the air in the room to be heated, where it is distributed thanks to a fan.

Compression phase

During this third phase of the cycle, the refrigerant, in gaseous mode, returns to the outdoor unit to become liquid again. For this reason, it is necessary to compress the gas, which goes to the compressor located in the outdoor unit, where it will be subjected to high pressure to change its state once again.

Condensation phase

In this last phase, the high-pressure steam circulates through the condenser. The heat escapes to the outside and the coolant condenses, turning back into liquid. Afterwards, the refrigeration cycle begins again.

What happens when the air conditioning is turned on?

When the air conditioning is turned on, the two machines, the exterior and the interior begin to work simultaneously, starting a hydraulic circuit formed by copper tubes, through which it circulates, that is, the gas, which plays the fundamental role of heat transfer.

Once the gas has travelled through the evaporator, it will return to the compressor and the cycle will begin again.

Does an air conditioner cool and heat in the same way?

You may be wondering at this point if the process is identical when the air conditioner produces warm air instead of cold air.

First of all, for this to happen an air conditioner with a heat pump is needed, therefore it is used for the winter season.