How Does Air Conditioning Work?

The first air conditioning system that modern units are based on was invented in 1902. Designed by Willis Carrier, an American engineer from Angola, New York, this groundbreaking innovation was initially intended to control humidity in a printing plant. However, its impact quickly expanded beyond industrial applications, revolutionizing how people live, work, and interact with their surroundings.

Today, the air conditioner is essential to daily life, shaping industries, urban development, and even global climate control strategies.

But how does air conditioning work? Let’s find out!

The Invention That Changed the World

In the early 20th century, industries faced significant challenges due to temperature and humidity fluctuations.

One of the most pressing issues was in printing, where excessive humidity caused ink to smudge and paper to warp. In response, Willis Carrier developed the first modern air conditioning system in 1902 for the Sackett & Wilhelms printing company in Brooklyn, New York. His design regulated both temperature and humidity by circulating air over coils filled with a cooling agent, a principle that remains at the core of air conditioning systems today.

This invention quickly attracted attention beyond the printing industry. By the 1920s, air conditioning entered department stores, movie theaters, and office buildings, transforming how businesses operated and how people experienced public spaces.

The introduction of centrifugal chillers in 1922 improved cooling system efficiency, which made it possible to equip larger buildings with air conditioning.

The technology further evolved in the 1950s, when residential air conditioning became widely available. This innovation reshaped urban development and enabled population booms in Sun Belt states in the U.S., where hot climates had previously limited growth. As homes, schools, and businesses embraced air conditioning, productivity increased, and indoor comfort became a standard expectation all around the world.

Today, we can’t even imagine our homes without them, and let’s not think about the non-cooled hospitals, schools, corporations, or shopping malls!

But despite its widespread use, many people don’t fully understand how these systems work. In the next section, we’ll explain the basic principles behind air conditioning and the science that keeps us cool.

The Basic Principle of Air Conditioning

Many people believe that air conditioners create cold air, but that’s not quite accurate. Instead, they work by removing heat and humidity from indoor spaces and transferring it outside. This process is based on the refrigeration cycle, a method similar to how refrigerators keep food cold.

At the heart of air conditioning is a special chemical called refrigerant.

This fluid can easily change from a liquid to a gas and back again, allowing it to absorb and release warm air fast. The entire cooling process relies on a closed-loop system where refrigerant cycles through different components, absorbing heat inside and releasing it outside.

So, How Does Air Conditioning Work?

To understand how air conditioning functions, let’s break it down into four steps:

1. Absorbing Heat (Evaporation) – Hot indoor air is drawn in and passed over the evaporator coil, which contains cold refrigerant. As the air is cooled, the refrigerant evaporates into a gas, cooling the air in the process.
2. Compressing the Gas (Compression) – The now warm refrigerant gas moves to the compressor, where it is pressurized, increasing its temperature even further.
3. Releasing Heat Outside (Condensation) – The hot, high-pressure gas flows into the condenser coil located outside. A fan blows outdoor air over the coil, which allows the hot air to dissipate. The refrigerant cools down and turns back into a liquid.
4. Starting the Cycle Again (Expansion) – The liquid refrigerant passes through an expansion valve, reducing its pressure and temperature before returning to the evaporator coil, where the cycle repeats.

This continuous process keeps indoor spaces cool while expelling unwanted heat outside. At the same time, air conditioners reduce humidity, making the air feel more comfortable even at moderate temperatures.

What are the Components of an Air Conditioner?

Air conditioners rely on a series of mechanical and chemical processes to regulate temperature and humidity. Modern AC units come in different shapes and sizes, but they all share the same fundamental components that enable efficient cooling:

1. Evaporator Coil – The Heat Absorber

The evaporator coil is located inside the home, usually in the air handler or furnace. This coil is filled with cold refrigerant, which filters out the hot air from the indoor air as it passes over the coil. This process lowers the air temperature while also removing excess humidity, making the indoor environment feel more comfortable.

2. Compressor – The Pressure Booster

The compressor, housed in the outdoor unit, acts as the heart of the air conditioning system. It pressurizes the refrigerant, raising its temperature and preparing it for the heat-release process.

Think of it like a pump that keeps the refrigerant moving through the system while increasing its ability to transfer heat.

3. Condenser Coil – The Heat Releaser

Once the refrigerant leaves the compressor, it enters the condenser coil, which is located in the outdoor unit. A fan blows outdoor air across the coil, allowing the refrigerant to release the absorbed heat into the surrounding air. As the refrigerant cools down, it returns to a liquid state and is ready to cycle back into the system.

4. Expansion Valve – The Temperature Regulator

The expansion valve (also called a metering device) controls the flow of refrigerant into the evaporator coil. Reducing the refrigerant’s pressure, causes the liquid to cool down significantly before entering the evaporator coil again. This step is essential for the refrigerant to absorb heat efficiently in the next cycle.

5. Refrigerant – The Heat Transporter

Refrigerant is the lifeblood of an air conditioning system. It circulates through the evaporator and condenser coils, continuously changing from a liquid to a gas and back. Different types of refrigerants have been used over the years, with modern systems moving toward eco-friendly alternatives that have a lower environmental impact.

6. Blower Fan – The Air Mover

The blower fan is responsible for circulating air throughout the home. It pulls warm air from inside the house, passes it over the evaporator coil for cooling, and then distributes the cooled air back into the rooms through the duct system.

7. Thermostat – The System Controller

The thermostat is the control center of an air conditioning system. It detects indoor temperature and signals the system to turn on or off to maintain the desired comfort level. Smart thermostats can optimize energy efficiency, learn household patterns, and adjust cooling cycles accordingly.

How the Air Conditioning Cycle Works (Step-by-Step)

Now that we’ve covered the key components, let’s take a closer look at how they work together to cool your home. The air conditioning process follows a continuous cycle of heat absorption and release, ensuring that indoor temperatures remain comfortable even on the hottest days.

To simplify things, we’ll break this process into two main stages:

1. Cooling the Indoor Air – The Cold Side of the System

The air conditioning process starts inside your home, where warm air is drawn in, cooled, and recirculated. Here’s how it works:

• Step 1: The thermostat detects a temperature rise.
  • When the temperature inside exceeds the set point on the thermostat, the air conditioner turns on.
• Step 2: Warm indoor air is pulled into the system.
  • The blower fan draws warm air through return ducts and passes it through an air filter, which removes dust and allergens.
• Step 3: The air moves over the cold evaporator coil.
  • As warm air flows over the evaporator coil, the cold refrigerant inside the coil absorbs the hot air, causing the refrigerant to evaporate into a gas.
• Step 4: Cooled air is circulated back into the home.
  • The now-cooled air is pushed through the ductwork and delivered to each room, lowering the indoor temperature.

At this stage, the air in your home is cooler and less humid, but the refrigerant has absorbed heat and turned into a gas. To continue cooling, it needs to be removed from the system, which brings us to the next phase.

2. Releasing Heat Outside – The Hot Side of the System

The heat that was absorbed indoors must now be transferred outside to keep the cycle going. This happens in the outdoor unit, where refrigerant releases the heat it collected.

• Step 5: The refrigerant gas is compressed.
  • The compressor squeezes the refrigerant, increasing its temperature and pressure. This step is crucial because the refrigerant must be hotter than the outdoor air for heat transfer to occur.
• Step 6: The hot refrigerant moves to the condenser coil.
  • The high-pressure gas travels into the condenser coil, where a large fan blows outside air over the coil, allowing heat to dissipate.
• Step 7: The refrigerant cools and returns to liquid form.
  • As heat is released outside, the refrigerant cools down and condenses back into a liquid.
• Step 8: The expansion valve lowers the refrigerant’s pressure.
  • Before re-entering the evaporator coil, the refrigerant passes through an expansion valve, which reduces its pressure and temperature, preparing it to absorb heat again.

The cycle then repeats continuously until your home reaches the desired temperature, and after that, the thermostat turns the AC off.

What Types of Air Conditioning Systems Exist?

Air conditioning systems come in different configurations to suit various home layouts and cooling needs. While they all operate on the same basic principle, removing heat from indoor air and releasing it outside, the way they are installed and distributed makes a big difference in efficiency and performance.

Learn more about the three primary types of residential air conditioning systems:

1. Split-System Air Conditioners (Central Air)

Best for: Homes with existing ductwork that need whole-home cooling.
How it works: Uses separate indoor and outdoor units connected by refrigerant lines.

Split-system air conditioners are the most common type of residential AC system in the U.S. and are often referred to as central air. They include:

• An outdoor unit that houses the compressor and condenser coil.
• An indoor unit (typically a furnace or air handler) that contains the evaporator coil and blower fan.
• Ductwork that distributes the cooled air throughout the home.

How does it work?

1. The evaporator coil inside the home absorbs heat from the air.
2. The refrigerant carries the heat outside to the condenser coil, where it is released.
3. The blower fan circulates the cooled air through ducts to every room.

Split systems come in single-stage, two-stage, and variable-speed options, and it’s easy to adjust different levels of efficiency and noise reduction.

Pros:

✔ Provides consistent and efficient cooling for the entire home.
✔ Works with heating systems for year-round climate control.
✔ ️ Filters the air, reducing allergens and dust.

Cons:

✕ Requires ductwork, which can be costly to install if not already in place.
✕ Uses more energy than ductless systems in some cases.

2. Packaged Air Conditioning Systems

Best for: Homes with limited indoor space or locations where rooftop installations are preferred.
How it works: All components (evaporator, compressor, and condenser) are housed in one outdoor unit.

Unlike split systems, packaged ACs combine all essential components into a single outdoor unit, which is usually installed on a roof or a slab near the foundation.

How does it work?

• Warm air from the house is pulled into the unit via return air ducts.
• The air is cooled as it passes over the evaporator coil.
• The blower fan then sends the cooled air back inside through the supply ducts.
• The unwanted heat is expelled outside via the condenser coil.

These systems are especially popular in the Southern and Southwestern U.S., where homes may not have a basement or attic space for an indoor unit.

Pros:

✔ Saves indoor space by keeping all components outside.
✔ Easier to install and maintain compared to split systems.
✔ Available in high-efficiency models with multi-speed blower fans.

Cons:

✕ Less efficient than split systems for whole-home cooling.
✕ More exposure to weather elements can lead to faster wear and tear.

3. Ductless Air Conditioning Systems (Mini-Splits)

Best for: Homes without ductwork, room additions, or areas needing zoned cooling.
How it works: Uses individual indoor air handlers connected to an outdoor unit via refrigerant lines.

Ductless systems offer a flexible and efficient cooling solution for homes where installing ducts isn’t an option. Each system consists of:

• An outdoor condenser unit (like in split systems).
• One or more indoor air handlers mounted on walls, ceilings, or floors.

Each indoor unit operates independently, allowing homeowners to set different temperatures in different rooms.

How does it work?

1. The indoor unit pulls in warm air, passing it over a cold evaporator coil.
2. The refrigerant absorbs heat and carries it outside to the condenser coil.
3. The cooled air is recirculated back into the room.

Some systems support multiple indoor units connected to a single outdoor unit, creating a zoned cooling effect.

Pros:

✔ No ductwork required – ideal for older homes or room additions.
✔ More energy-efficient than central air (no duct losses).
✔ Allows for individual temperature control in different rooms.

Cons:

✕ Higher initial cost per unit compared to split systems.
✕ Not as aesthetically pleasing as hidden ductwork.

Knowing how it works may help you with using your air conditioning system more efficiently, extending its life, and keeping energy costs down. Don’t forget to regularly book air duct cleaning, for keeping your AC system healthy and efficient.