Type to search

The Principles of Air Conditioning: How Air Conditioners Work


An air conditioner is integral to our modern lives, providing comfort in homes, offices, and vehicles. The ability to regulate temperature and humidity has revolutionized the way we live and work. But how do the different components of an AC system function? 

If you’re curious about how an air conditioner works, you’re in luck. Here, we will discuss the fundamental principles of air conditioning and how these systems create a comfortable indoor environment.

How Does Air Conditioning Work?

how do air conditioners work

Air conditioning systems function based on the principles of thermodynamics and fluid dynamics. The key to an air conditioning process lies in the refrigeration cycle, a continuous process that transforms a refrigerant from a gas to a liquid, resulting in cool air or hot air.

This cycle relies on the physical properties of a refrigerant gas, a substance that can easily change between a gas and a liquid. The cycle consists of four main stages:

  1. Compression: The compressor raises the temperature of the refrigerant by pressurizing it.  
  2. Condensation: The condensing process starts once the hot, pressurized gas flows to the condenser, releasing heat and transforming into a high-pressure liquid state.
  3. Expansion: The high-pressure liquid moves through a cooling agent, reducing its pressure and temperature. As it passes the cold cooling coil, the cold refrigerant passes from the copper tubing to the outdoor part of an AC. 
  4. Evaporation: The cool liquid enters the evaporator as the air absorbs heat from the refrigerant surrounding air and then turns back into a low-pressure gas. Then, the hot and cold refrigerant travels back inside to repeat the cycle. 

As warm air glides over the evaporator coil, the moisture condenses on the coil and is drained away. This dual functionality ensures a comfortable indoor environment by lowering the climate and maintaining optimal humidity levels. An AC cools the room and removes heat at the same time. 

Remember, residential air conditioners do not take in outside air or purify air. Only industrial units can take in outdoor air temperature and cycle it into cold air. Do note that there are different air conditioner systems. Take, for example, a ductless air conditioner that works differently than a modern air conditioning system.

What are the 4 Basic Components of an Aircon?

Understanding the four fundamental components of an air conditioning system is crucial to grasping its inner workings:

Compressor: The Powerhouse of the System

At the heart of every air conditioning system lies the compressor, a dynamic component often called the system’s powerhouse. The compressor is essential in the refrigeration cycle, acting as the catalyst for the entire cooling process. 

Operating like the beating heart of the system, it takes in the refrigerant in a low-pressure, low-temperature gaseous state and compresses it. This compression increases the pressure and temperature of the refrigerant, setting the stage for the subsequent cycle stages.

Condenser: Releasing Heat to the External Environment

The condenser, another indispensable component, takes center stage in the next phase of the refrigeration cycle. It is responsible for a crucial task—releasing the absorbed heat from the refrigerant to the external environment. As the high-pressure gas from the compressor enters the condenser, it transforms, transferring heat. 

The condensing coil facilitates the release of unwanted heat inside, causing the refrigerant to transition from a high-pressure gas to a high-temperature liquid refrigerant. This critical step ensures the system can effectively expel the heat absorbed from the indoor environment.

Expansion Valve: Regulating Flow for Optimal Performance

A key player in maintaining the delicate balance of the refrigeration cycle, the expansion valve regulates the refrigerant’s flow. This valve, positioned strategically between the condenser and the evaporator, acts as a gatekeeper, carefully controlling the refrigerant that enters the evaporator. 

Doing so facilitates a reduction in both pressure and temperature, preparing the refrigerant for its role in the evaporator. This precise regulation ensures optimal system performance and sets the stage for the efficient cooling of indoor spaces.


The evaporator, often considered the magic chamber of the system, is where the cooling process culminates. Positioned within the indoor unit and connected to an air handler, the evaporator absorbs heat from the surrounding indoor air. As the low-pressure liquid refrigerant enters the evaporator coils, it undergoes a phase change, transforming into a low-pressure gas. 

This process effectively extracts heat from the air inside your room, cooling the air and creating the refreshing breeze we associate with air conditioning. The now-warmed refrigerant is then cycled back to the compressor to begin a new refrigeration process. This component then uses a blower fan to blow the cold air into the air ducts. 

How Do Different Air Conditioning Systems Work?

Types of air conditioners

While the refrigeration cycle is a fundamental aspect of most air conditioning systems, various types of air conditioning systems may have different configurations and additional features. However, they still operate on the same basic premise. 

We’ll explore some AC systems and how they produce cold air inside living spaces.  

Split System Air Conditioners

Split AC systems have different parts. They have an indoor unit called an evaporator and an outdoor unit called a condenser.

The indoor part contains the evaporator coil and a fan. It is installed inside the room to be cooled. The outdoor part houses the condenser coil, compressor, and another fan. Refrigerant lines and electrical cables intertwine the indoor and outdoor units.

The indoor unit collects heat from the indoor air and transfers it to the outdoor part, where it is released. The cold air is then circulated back into the room. Split AC systems are versatile and can be used for cooling and heating.

Window Air Conditioners

Window AC units are self-contained systems housed in a single box typically installed in a window or a specially designed opening in a wall.

They have different components, like a built-in evaporator, condenser, compressor, and expansion valve. The entire system is enclosed in a compact unit.

These units work by taking in hot air from the room, passing it over the cold evaporator coil to cool and dehumidify it, and then expelling the heat outside through the condenser coil. The cooled air is then circulated back into the room.

Central Air Conditioner System

Central AC systems are complex and typically include a central unit containing the evaporator, compressor, condenser, and a network of ducts to distribute air throughout the building.

The central unit is usually located outside the building. Air is cooled in the central unit, passes through the fan coil, and then distributed through the ductwork to various rooms.

Central AC systems operate similarly to split AC systems but are designed for larger spaces. They offer the advantage of consistent and even cooling throughout the building.

Ductless Mini-Split Systems

Similar to split AC systems, ductless mini-split systems have an indoor unit and an outdoor unit. The difference is that multiple indoor units can be connected to a single outdoor unit.

A ductless unit operates similarly to traditional split AC systems, with the added flexibility of zoning, allowing users to control the temperature of different rooms independently. You can even put one in your garage without the hassle.

How Do Air Conditioners Heat Air?

Interestingly, air conditioners have a dual function. While they are primarily known for cooling, they can also heat air. During colder months, the refrigeration cycle is reversed through a process known as the heat pump cycle. It collects heat from the outside air and releases it into the indoor space, providing warmth even in chilly weather.

How Does an Air Conditioning Unit Work During Summer?

Buying an air conditioner in the Philippines

Air conditioners are crucial in maintaining a comfortable indoor temperature during a hot summer. The unit draws warm air from the room, and as this air passes over the cold evaporator coils, the heat is absorbed. Simultaneously, the moisture in the air condenses, contributing to the dehumidification process. The cooled and dehumidified air is then circulated back into the room, creating a pleasant environment.

The air conditioning unit undergoes a heat exchange process. Air conditioners rely on heat exchange to cool indoor spaces. The evaporator and condenser coils play a crucial role. 

The evaporator coil collects heat from the indoor air. The condenser coil, situated in the outdoor unit, releases the absorbed heat outside. This exchange of heat is what makes the indoor environment cooler.

JP Reyes

JP has been in the aircon industry for almost as long as he has been alive. As a child JP would help his tatay fix aircon units at their junk shop in Cavite. After graduating UP in the early 2000's, JP then started his own Aircon servicing business and within 5 years had 10 shops in 8 different cities. Fast forward to today and JP brings all his experience and expertise online to give readers trustworthy advice and reviews about Air-conditioning buying, servicing, cleaning and repair in the Philippines.

  • 1