how do air conditioners work

How Do Air Conditioners Work?

  • July 22, 2021
  • By MR COOL

Nearly 90% of all homes in the United States rely on air conditioning to provide comfort in hot weather. More than one-quarter of all AC owners report using their equipment continually through the summer. Compared to alternative home cooling methods, air conditioning is by far the most widely used and effective. But have you ever wondered how it works?

There several different types of indoor air conditioners, each one operating differently from the next. Regardless of the system, however, the basic air conditioning process and chemical reactions involved are the same.

Read on to learn about the invention of air conditioning, the different types of refrigeration and air conditioning technology and how AC works.

The History of Air Conditioning

With so many people today actively relying on air conditioning as an essential part of life, it might be difficult to imagine a time when it was a luxury. When room air conditioners debuted, however, many people were hesitant to believe they could ever work. 

Where and When Was Air Conditioning Invented?

Although he was not the creator of air conditioning as we know it today, Dr. John Gorrie was the first to patent an indoor cooling system in the 1840s. To relieve his patients and neighbors from dangerous heat, he crafted a cooling machine that produced ice using power generated by water, a horse and either wind-driven sails or steam. 

Just a few decades later in 1907, engineer Willis Carrier was working to solve Brooklyn, N.Y.’s Sackett-Wilhelms Lithographing and Publishing Company’s problem with wrinkled magazine pages, caused by excessive indoor humidity. As he experimented with different methods and patents, he eventually arrived at the earliest version of the modern AC unit, which he called the “apparatus for treating air.” Carrier’s setup functioned by either heating or cooling water to humidify and dehumidify the air, specifically in textile mills.

Soon, Carrier realized what an impact his new mechanism could have on other businesses and households. Although many were skeptical and wary of the new technology, air conditioning began to grow in popularity. At first, businesses used it almost exclusively, but the public got to experience the comforts of cooled air as soon as nickelodeons began using air conditioning to enhance movie viewers’ experience. Initial systems were still bulky and quite expensive to produce, so they were not yet a staple in the American home.

By the end of World War II, the media were touting air conditioning units as a modern convenience that would soon be cheap enough for every homeowner to enjoy. Sure enough, by the late 1960s, air conditioning units were commonplace in newly built homes.

Different Types of Air Conditioners

Various air conditioning systems are suitable for different types of homes and businesses. As you consider the best cooling method for your building, take into account your initial and ongoing budget, available space and priorities, such as noise level or environmental impact.

Ductless Mini-Splits

Ductless mini-splits do not send cooled air through ductwork, like most air conditioning systems do. Instead, single-zone mini splits use an individual fan and evaporator to cool and dehumidify each room separately. Multi-zone units can cool several rooms of a home with ease. 

Because mini-splits do not use ducts, they’re very energy efficient. In forced-air systems, duct losses due to poor installation can result in more than 30% of the system’s total air consumption. They function by using a compressor or condenser system on the outside of the home, an indoor air-handling unit and a conduit that connects them. These AC units operate quietly and typically get installed near the top of a wall or mounted from the ceiling, making them ideal for small areas. That’s why, in addition to single-family homes, you’ll likely find mini-splits in apartment buildings or other spaces without enough room for ductwork. 

Other installation options include standing or floor-model mini-splits, as well as compact four-way cassette types. One look at a mini-split AC system diagram, however, and you’ll see that no matter where you have your unit installed, they operate similarly.

These air conditioners are a cinch to work with and put in place. MRCOOL even offers several DIY mini-splits with pre-charged linesets, so you can quickly install them yourself without specialized training or equipment.

DC Inverter HVAC Systems

DC inverter HVAC systems work by first sending electricity through an inverter, which regulates the refrigeration and temperature. Because you can adjust the refrigerant capacity as needed, DC inverter systems are highly efficient. This type of operation means no extreme fluctuations, which can waste energy. 

DC inverter HVAC units are quiet and cost-efficient, making them suitable for any home or business owner who wants quick and reliable cooling while keeping their energy expenses low.

Central Air Systems

Central air conditioning systems use supply and return ducts to carry chilled air from the air conditioner throughout the house, which gets output through registers in the walls, floors and ceilings. As the air travels, it naturally warms before returning through the vent registers and into the ducts, where the central air conditioning system re-cools it. These systems are either split or packaged.

Split systems have an outdoor cabinet that houses the condenser and compressor and an indoor cabinet with the evaporator inside. Packaged units have one outdoor cabinet — usually located on the flat roof or solid foundation by a home or business — that houses the evaporator, condenser and compressor elements. 

If you look at a central air conditioning system diagram, you will note two sets of coils: evaporator and condenser. Through the refrigerant that flows through these coils, central air systems can cool an entire home evenly and with quiet operation.


For those seeking a safe, environmentally sound and low-maintenance cooling system, geothermal air conditioning is an excellent option. Geothermal heat pumps use the temperature of the earth to cycle water or refrigerant through underground piping, which transfers heated or cold air through a home. Compared to traditional HVAC systems, geothermal units can cut a building’s energy consumption by half

MRCOOL GeoCool air conditioning is a virtually noise-free, simple-to-use system with minimal components, making it long-lasting and reliable. GeoCool geothermal air conditioning is also free of hazardous carbon dioxide, carbon monoxide and greenhouse gases. 

Packaged Terminal Air Conditioners (PTAC)

PTAC units are affordable and efficient systems, often found in places like hotels or homes without central air. PTACs can condition the air in a space using a refrigerant to cool a series of coils, later exhausting heat and humidity outside. PTACs are self-contained, meaning inhabitants of each room can control the temperature to reach their desired level of comfort. 

This level of containment makes them cost- and energy-efficient, because only occupied rooms will require and operate a PTAC. MRCOOL PTAC units also feature quiet operation and environmentally friendly refrigerants.  

The Ins and Outs of Air Conditioning

How does air conditioning work? Although operating an air conditioner is as straightforward as adjusting the thermostat, AC units must undergo several processes to cool a room. The method relies on the fact that refrigerants, comprised of chemicals, convert quickly between gaseous and liquid states. During these transformations, the refrigerant absorbs heat from the air indoors and expels it outside. The five primary components of air conditioning systems — the evaporator, compressor, condenser, expansion valve and thermostat — help this process along.

Each type of air conditioning unit functions a little bit differently, but the principles are the same. For example, here is how a split-system central air unit cools a room or building.

Evaporator Coils Absorb Indoor Heat 

So, how does AC work? The process takes place both indoors and outdoors.

Inside the home, vents draw in warm air from a room and push it into the evaporator coil part of the AC unit. Evaporator coils consist of copper, steel or aluminum, as these are the best heat conductors. With the help of built-in metal fins, these evaporator coils absorb the heat from the air.  Meanwhile, a blower moves that cold air into ducts, if applicable. Once inside the air ducts, the now-cooled air gets distributed throughout the building.

It’s essential to note that, over time, evaporator coils can collect dust or develop pinhole-sized leaks. For this reason, regular maintenance is crucial for the efficacy and longevity of your air conditioning unit. Evaporator coils can also freeze without constant, adequate airflow. To ensure airflow remains uninterrupted, change your air filters regularly and keep the vents in your building open. 

An Outdoor Blower Moves the Air to the Compressor

Outside the building, a blowing fan helps the air conditioning unit intake warm air and moves it along to the compressor. As the air moves, the refrigerant inside the unit consumes the heat and transforms from a liquid to a high-pressure gas. 

There are different types of refrigerant, each regulated by the EPA. MRCOOL primarily uses R410A refrigerant, which is more environmentally friendly than others.

The Compressor Changes the Refrigerant Into a Gas

Once the now-vaporized refrigerant travels through the suction line and reaches the compressor, it undergoes a tight compression process, which causes the temperature to rise. This process usually involves a built-in piston, which moves back and forth to draw the refrigerant in before compressing the molecules. By the time the refrigerant exits the compressor through the discharge line, it is a hot, high-pressure gas. 

As with the evaporator coils, condenser coils require regular maintenance and upkeep, as well as adequate airflow, to remain fully functional.

The Refrigerant Moves to the Condenser and Turns Back Into a Liquid

The hot refrigerant vapor then moves to the condenser element — also located outdoors — which consists of hot coils that reject the heat in the refrigerant, allowing the warmer outside air to absorb it instead. Through this process, the refrigerant now changes back to a hot, high-temperature liquid.

Once this hot liquid refrigerant meets the expansion valve, the temperature and pressure each decrease. This process is what produces the cool air we come to expect from our air conditioning systems. 

A Fan Distributes the Cool, Filtered Air 

Afterward, the refrigerant once again moves back to the evaporator, where the air conditioner fans blow the cooler air into the building. Most air conditioners have built-in systems that filter out any impurities and particles as the fan expels and circulates the cold air.

There are a few different types of air conditioner filters.

  • Fiberglass: Fiberglass air conditioner filters are disposable, flat and consist of layered fiberglass laid on a metal frame. They are typically the most affordable option, and will adequately filter out dust and pollutants.
  • Pleated: Instead of laying flat like fiberglass filters, pleated filters consist of layered fabric or cotton. These pleats make them excellent at filtering sediment and pollutants from the air.
  • HEPA: High-efficiency particulate air filers — also known as HEPA filters — are a staple of hospitals or homes with residents who suffer from extreme allergies or respiratory concerns. They are the most effective at absorbing even the smallest pollutant molecules from the air, including those caused by tobacco smoke. Please note: Because they provide extreme filtration, they can impede airflow at times. Therefore, you should only use a HEPA filter in an environment when air quality is crucial.
  • Reusable: These filters are similar to flat fiberglass filters, only instead of being disposable, you can easily remove, clean and replace them. This quality makes them a more substantial initial investment, but less costly over time. When washing a reusable filter, you must abide by all manufacturer instructions and allow ample time for them to dry before replacing to avoid mildew growth.

Many manufacturers implement built-in air conditioner filters. For optimal performance, you should always follow manufacturer instructions for the best filter type for your specific air conditioning unit. Inspect your air filters regularly. When they become dirty, it’s time to replace them. Depending on the size of your home, quality of your air and number of pollutants involved, you might need to do this anywhere from every few weeks to every few months.

The Thermostat Controls Cool Air Distribution

The air conditioner unit repeats this process until the room or building reaches the desired temperature set on the thermostat. Smart thermostats are an ideal option for controlling the temperature of a building because they automatically adjust the temperature for optimal performance and energy saving. Programmable smart thermostats can also adhere to a schedule, adjusting the temperature to be cooler overnight and while you’re away, and more comfortable during the day. A small change like this can save as much as 10% on energy costs per year.

With Wi-Fi-enabled smart thermostats, you can also monitor your energy usage. You can even control a smart thermostat from your phone, making them the ideal choice for those who want to save both time and money.

Learn More About Becoming a MRCOOL Reseller

MRCOOL provides innovative, state-of-the-art heating and cooling solutions, including the only DIY® HVAC systems available on the market. 

If you’re ready for a cool, comfortable home, find a MRCOOL dealer near you. Are you interested in working with MRCOOL products? Tell us a little bit about you and your business, and we’ll get back with you with everything you need to know about being a MRCOOL representative.

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