How Does Central Air Work? An Informative Guide

Air conditioning is a luxury we take for granted here in the U.S. A recent survey by the Energy Information Administration found that 87%, or 100 million homes have some form of air conditioning, whether it be central air or window units.

In hotter climates like in the Southwest, however, central air is king. Fighting against the insanely hot temperatures you’ll find in Arizona, central air is the only way to compete. By turning our homes into, essentially, giant refrigerators, we greatly improve our quality of life.

If you’ve ever found yourself asking “how does central air work?” You’re in luck. This article will take you through everything you need to know about the machinations of central air conditioning.–>

How Does Central Air Work?

When we mentioned that using a central air unit is like turning your house into a refrigerator, we weren’t kidding. A central air system uses all of the same components a typical refrigerator does, but on a much larger scale.

To answer the question “how does central air work?” We have to understand these components and what they do.


Refrigerant is a substance that runs through your system’s cooling tubes and changes from a gas vapor to a liquid as it collects heat from your house and ejects that heat outdoors.

It’s a unique substance that has a low boiling point and changes from a liquid to a gas at lower temperatures than most other liquids. This is important because it allows this system to cool your house safely, without worrying about a pipe bursting with hot steam.


The compressor can be considered the heart of your central air system, pumping the refrigerant through all of your unit’s components in a big circuitous loop.

The refrigerant enters this compressor as a low-pressure warm vapor and leaves it as a higher-pressure hot vapor.


Immediately from the compressor, your hot-vapor refrigerant moves to the condenser. Here, the vapor is cooled down as it moves through what are known as “condensing coils.” Like a car radiator, the condensing coils have thin metal fins that conduct heat from the coils while a condenser fan blows on over the fins to speed up the cooling of the vapor.

As it cools, the refrigerant turns from a vapor to a hot liquid before moving on to the expansion valve.

All of the components listed so far – the compressor, condenser coils and condenser fan – are all located in that big noisy box outside next to a wall of your house. These components, all together, are called a condensing unit.

Expansion Valve

Here is where the real cooling happens. At this stage, the hot liquid refrigerant gets pushed through a small tube at a high pressure into this open valve, or chamber. As this happens, a natural process of liquid-like gases occurs: as a gas expands, it cools down.

So once through this valve, the refrigerant leaves as a low-pressure cool mist instead of a hot liquid.

Evaporator Coil

This low-pressure cool mist that left your expansion valve now runs through the evaporator coil, that is located in the plenum of your furnace. The plenum is just a technical term for the big metal box that sits above the furnace or air handling unit behind that door in your house that connects to the air ducts.

It is also commonly placed in basements or attics.

At this stage, the hot air in your house blows over the evaporator coils, heating the refrigerant inside it. But during this process, the air and the coils exchange their temperatures, so now the air is cool and it is then circulated through your house through the air ducts.

As the refrigerant heats up, it begins boiling (remember it has a low boiling point) and turns back into a warm vapor. This vapor then travels back outside to the compressor and the cycle is started again.

Further Explanation

Hopefully, this has given you a general sense of how central air conditioners work.

But if you’re still not sure you know how to answer the question “how does central air work?” Allow us to provide a concrete example.

Let’s say it’s a hot 95-degree day outside. You’ve been out all day so the air conditioner has been off and the thermostat currently says that the internal temperature of the house is at 86 degrees.

You flip the thermostat on and set it to 74 degrees. Then what happens?

Well, the thermostat triggers a fan in the air handling unit that draws in air from your house through a set of ducts that specifically carry warm air and blows it over the evaporator coils, cooling the air. That air is then pushed through your cool air ducts, blowing that air back through your house.

This cold air is then drawn back into your air handling unit, being cooled even further by the evaporator coils.

This process happens over and over again until the room air has cooled to the temperature specified by your thermostat. Once that happens, the thermostat tells the air-handler fan and the condensing unit outside to turn off.

Once the temperature of the air in your house goes above your desired temperature, the air conditioning unit turns back on again, repeating the process.

Need Help With Your A/C?

As you can see, the answer to the question “how does central air work?” is not a simple one. Central air systems are very complex, but they cannot be beaten when it comes to delivering cool air throughout your house.

If you are fortunate enough to have central air in your home, but it’s on the fritz, consider giving us call. We’re the best central air repair experts in Arizona. Whether you need small fixes or a require replacements for major components, we’ve got you covered.

As we’ve said, central air units are complex, and you shouldn’t have to navigate them on your own.


As one of the best air conditioning companies in Chandler, the HVAC experts at Mark Daniels Air Conditioning & Heating are dedicated to providing exceptional air conditioning replacement, repair, and inspection services. If your AC isn’t working properly, get in touch with us today!

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