How Do Air Conditioners Work?

Air Conditioning Guide

On hot, humid summer days, AC is a much-appreciated comfort — and many of us even consider it a necessity. If you’re shopping for an AC system but don’t know which type would be best for your house, we’ll equip you with everything you need to know, including how air conditioners work, how to pick the right size and how to fix common air conditioner issues.

How Does AC Work?

How do air conditioners work? Air conditioners come in many forms, but they all function in the same fundamental way. They provide a home or other enclosed space with cold air by removing the heat and humidity from the air inside. They then return this cooled air to the inside, transferring the unwanted humidity and heat outside.

Standard AC and cooling systems use a specialized chemical known as a refrigerant and feature three primary components — the compressor, the condenser coil and the evaporator. These parts help turn the refrigerant from a gas to a liquid, then back again.

Below, we’ll describe the cycle an air conditioner goes through to cool your home.


  1. The compressor heats the refrigerant: The compressor increases the temperature and pressure of the refrigerant, which is in a gas state. The refrigerant then travels into the condenser coil.
  2. The refrigerant becomes a liquid: When the refrigerant reaches the condenser coil, it turns into a liquid. Then, it travels back indoors, where it goes into the evaporator coil.
  3. The refrigerant evaporates: In the evaporator coil, the liquid refrigerant will evaporate, cooling the indoor coil.
  4. A fan blows indoor air through the now-cold evaporator coil: The heat in the home gets absorbed by the refrigerant. As the cooled air travels throughout the indoor space, the evaporated, heated gas travels back outside and goes back into the compressor.
  5. The system releases heat outside: As the refrigerant releases heat, it returns to a liquid state in the condenser coil. This cycle will continue until the indoor space reaches the temperature set by the thermostat.


Central Air

When learning about how air conditioners work, it’s essential to note that many North American homes use a split-system air conditioner, frequently called “central air.” These systems don’t merely cool the indoor air — they can also control air quality, humidity and airflow.

A central air system generally comes with the following features.


  • Thermostat: This device controls the system’s operation.
  • An outdoor unit: The outdoor unit houses the condenser coil, compressor and fan.
  • An indoor unit: Generally either a fan coil or furnace, the indoor unit contains the evaporator coil and the fan that moves the cooled air.
  • Copper tubing: A series of tubes enables the refrigerant to travel between outdoor and indoor units.
  • Expansion valve: The expansion valve regulates how much refrigerant goes in the evaporator coil.
  • Ductwork: Ductwork circulates the cooled air throughout the rooms of a home via vents, then back to the unit.

Air Conditioner Types

As houses come in various sizes and shapes — ranging from mobile homes to mansions — residential AC systems are also available in many configurations and styles. There are three main types — split-system, package and ductless — each of which has specialized applications. However, they all perform the same essential function — cooling a home. The best fit for you will depend on various factors, including your location, how you use it, your home’s size and its physical limitations.

Here, we’ll give you a basic overview of each type.

1. Split-System


Split systems are central air systems that feature an indoor and outdoor unit. Its indoor unit, which usually features a fan coil or furnace, includes an evaporator coil and a blower fan, which circulates air through your home. The outdoor unit houses the condenser coil and compressor.

Split-system air conditions come in a wide range of options, including single-stage, more efficient, two-stage models and the most energy-efficient, quietest multi-stage models. Split-system AC models offer reliable, consistent temperature control for the whole house. What’s more, they can keep your indoor air cleaner because they also have an air filter.

2. Packaged

Package systems are central air systems that house the compressor, blower fan and evaporator coil in one single unit. These systems are ideal when there’s not enough closet or attic space for a split system’s indoor unit. They also work well in places that would usually have AC systems installed on the rooftop.

Similar to a split system, a package system will pull warm air from your home, then through return air ducts and into an evaporator coil. The warm air passes through the evaporator coil, and supply air ducts deliver the newly cooled air to all parts of your home. As with split systems, a condenser coil releases unwanted heat outside.

Packaged systems offer various options for improved energy efficiency. You can get a system with two stages or only a single stage. Models with enhanced efficiency often feature blower fans with multiple speeds. In the U.S., this type of system is most prevalent in the South.

3. Ductless

Unlike central air systems, ductless air conditioning units provide chilled air for specific rooms or zones of a home. Their installation is less invasive because — as the name suggests — this system does not rely on ducts to deliver cool air.

They are similar to split systems in that they have an outside unit and a minimum of one indoor unit inside, connected with copper tubing. However, a ductless unit only provides chilled air to one room at a time. There is lots of flexibility when installing the indoor unit — it can be on the ceiling, wall or floor. A ductless system may also include several indoor units that connect to a single outdoor unit. However, no matter how many indoor units there are, they still operate much like split systems — the inside unit houses the evaporator coil and blower fan that pulls unwanted warm air from the room through the evaporator coil, returning the cooled air to the room.

Refrigerant travels through copper tubes to the outside unit, which houses the condenser and compressor. Here, the heat from inside escapes through the condenser coil. The refrigerant goes back to the inside unit, where the cycle repeats.

Ductless systems allow you to cool specific areas of your home. They’re also like zoning systems in that you can have individual control over each room’s climate. For instance, if you like your office warmer but your bedroom cooler, you can install a ductless unit in both rooms and set the specific temperature you want for each.

How to Choose an Air Conditioner

By now, you understand the different types of air conditioners, and you may already know which will work best for your situation. However, when shopping for the best model, you should consider several features.


  • Noise: When shopping for a model, make sure to investigate how loudly it operates. Some models are so quiet that the only thing you may hear is the fan humming, whereas others are so noisy that they distract everyone when set on high.
  • Window location: Window AC units are generally better at blowing air in a single direction, which can be problematic if the window doesn’t have a central position on the wall. To cool uniformly, the system will need to direct air to the room’s center. If you’re installing a unit in a non-centered window, make sure it can blow air at different angles.
  • Type of windows: Keep in mind that most units’ design is best for installation in double-hung windows. If your windows are casement, consider getting a through-the-wall AC unit instead.
  • Filter location: Note the filter’s location on the units you’re considering. When installed, will you be able to access it easily? You will need to clean your filter regularly to keep your unit in top condition.
  • Intelligent cooling: Some new AC models allow you to control them remotely from a device.
  • Warranty: Some models offer better warranties than others. Check the manufacturer’s website for warranty info on the model you’re thinking about buying.

Calculating the Right Size

Before you start considering features and costs, determine the size of the unit you’ll need for the areas you want to condition and figure out where you’ll install the unit.


When we talk about “size” regarding air conditioning, this doesn’t refer to the appliance’s physical dimensions, but its cooling capacity, as measured in British thermal units. Whether you’re looking for a central air system or window air conditioner, you’ll enjoy the highest efficiency if you pick a unit based on the size of the room or area you want to cool.

To calculate the BTUs you need, you’ll first need to know the area of the room you want to cool in square feet. Multiply the room’s width by its length. Then, multiply the number you get by 25 BTU. This formula will allow ample cooling, regardless of the weather conditions outside.

Let’s say the room you want to cool is 15 feet wide by 20 feet long. Multiplying 15 by 20 equals 300 square feet. Multiplying that number by 25 BTU equals 7,500, the minimum capacity required to cool your room.

Common Air Conditioner Problems and Repairs

Like any other appliance, air conditioners occasionally experience problems that affect their performance. This section will cover some of the most typical issues encountered and how to fix them.

Indoor Water Leaks

If you notice water leaking out of your AC’s indoor unit, you are overdue for maintenance. If an air conditioner leaks water, it may indicate that algae or mold have clogged the system’s condensate drain, causing water to back up into your house. Another possible source of the problem is that the condensate pump is broken and needs replacing.

To fix a water leak, you can call a technician or try fixing it yourself if you feel comfortable doing so. You can unclog the condensate pipe using a dry or wet vacuum. Another possible solution is to pour five ounces of vinegar down the drain, which will kill algae and mold growth. The drain pipe’s location varies from unit to unit, so make sure to look at your user’s manual beforehand.

Outdoor Water Leaks

During hot weather, you may notice water puddles forming outside directly under your AC’s compressor. There are several possible causes of this problem, including improper installation, a broken condensate pan, a dry air filter or a faulty AC seal.

If you notice this problem, turn your AC unit off immediately and disconnect its power supply. If you fail to give this issue immediate attention, it may worsen and compound your problems. We recommend hiring a professional to fix this issue.

Refrigerant Leak

As you now know, AC refrigerant is responsible for chilling the air in your AC system. However, this refrigerant might occasionally leak, which will reduce your AC’s efficiency. A refrigerant leak can also harm the surrounding environment.

If the leak is minor, you will need to top up your refrigerant and perform a minor repair. If the leak is more severe, you may need to change the entire network. When you recharge your refrigerant, make sure not to overcharge or undercharge it, which may prevent your system from performing at its best.

Dirty Filter

The filter on your AC is essential for keeping your airflow clean and pollutant-free. If your air filter gets clogged, this will restrict airflow, decreasing your system’s efficiency and its ability to effectively cool your air. See how often your manufacturer recommends cleaning or changing your air filter.  If you have a smart AC controller, you can quickly check your system’s status.

If anyone in your household struggles with allergies, asthma or other respiratory issues, try checking and cleaning your air filter at least every three months. If you have pets, you should change your filters even more frequently, as lots of fur and dander will get caught in your filters.

Frozen Evaporator Coil

If your AC unit stops working altogether, a frozen evaporator coil may be to blame. This coil will freeze if the AC unit does not receive the air it needs to operate. If your evaporator coil freezes, your AC may also freeze up as a result and may stop working altogether. Ice sheets may even start to build up on your coil.

To diagnose the issue, first, assess the damage. Let your evaporator coil thaw, which will happen on its own if you are not using your unit. Make sure to unplug the power connection first. Evaporator coils generally take around 24 hours to completely thaw, though you can use a hairdryer to speed the process — be careful not to overheat your coil. In most cases, you will need a professional to fix the issue.

Contact Us About Our AC Services

As a Harrisburg resident, you know how essential reliable AC is during the summer months. When it gets hot, you need to know your AC system will deliver a dependable performance without increasing your utility bills.

At David LeRoy Plumbing, we can help. Whether you need to update your AC unit or need your existing unit repair, don’t hesitate to reach out to our team of HVAC specialists.


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