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The Ultimate Guide to How AC Works

For most of us, our interest in AC ends when we feel cool. We switch the thermostat to the temperature we want, and feel a sense of gratitude when we hear the blower kick into action. But after that, we stop thinking about it.

And that’s understandable. The whole point of modern technology is to make life easier. We’re not supposed to care how it works, for the most part.


Of course, when our AC breaks, we suddenly become very interested in how it works. Unfortunately, outside of HVAC professionals, the average population has very little idea of how AC systems work.

This guide will walk you through exactly how your AC system works. Not only is it actually quite interesting, but it can help you pinpoint problems, which can potential save you time and money with repairs.

Of course, you shouldn’t try to work on your own system without knowing all of the safety measures that must be taken in order to prevent electrical shock, refrigerant inhalation, and explosions. Leave that to the professionals.

How Refrigerant Works

Perhaps the most enigmatic element in our AC systems is the mysterious substance known as “refrigerant”. Of course, taking a closer look reveals its secrets, and it’s not as complicated as one might think.

Refrigerant is defined as any fluid that is used to cool things down. By that definition, you can argue that a cold glass of water that cools you down after a hot day outside is refrigerant.

The refrigerant used in your AC system is almost certainly either R-22 or R-410A. Let’s break these down.


R-22 is most commonly known as freon. It was used as the standard refrigerant in almost everything for decades, including HVAC, cars, and aerospace. After some research, scientists discovered that freon is not exactly environmentally friendly – namely, it began degrading the ozone layer in the upper atmosphere, which contributes to climate change. Not good.

So, we phased it out. The next iteration is called R-410A, and it’s considerably better for the environment than freon. After 2020, the United States government will no longer allow the importation or manufacture of freon. While this is a necessary countermeasure against climate change, it will have some adverse side effects.

Many older HVAC systems still rely on freon. With the manufacture and import ban, it will become much harder to find it, which means your system will be more expensive to repair. You may have to have it modified or replaced in order to keep your AC going.

We should note that R-410A isn’t perfect. It’s still a hydrofluorocarbon, which makes it non-ideal for the environment. It will likely be phased out and replaced with an even newer refrigerant called R-32. R-410A has a fraction of the environment impact of freon. Similarly, R-32 has one-third of the environmental impact of R-410A.

Constant progress and technological innovation are proving to be the best way to combat climate change while maintaining our way of life.

But how does refrigerant make the air in your system cold? Let’s explore that process in depth, because it’s the single most important feature of your system. Without it, there’s no cold air. No cold air, and you have a pretty nasty summer.

Refrigerant relies on a scientific principle called the Ideal Gas Law. In simple terms, it explains the relationship between the pressure and temperature of so-called “ideal gasses”. Ideal, in this context, means a gas that is not affected by interparticle forces and interactions. No ideal gas exists outside of theory. Refrigerants are used because they behave closest to an ideal gas (although, technically, they are not ideal).


According to the Ideal Gas Law, when a gas expands, it cools down, provided the number of atoms in a given vessel remains the same. For refrigerants under the right conditions, this effect is quite drastic. In your HVAC system, the temperature of your refrigerant plummets to 40 degrees Fahrenheit, purely through the Ideal Gas Law.

But this doesn’t happen on its own. Refrigerant only works in conjunction with the rest of your HVAC system. Let’s get into that.

How Your AC System Uses Refrigerant to Cool Down Your House

Your AC system consists, very basically, of a compressor, some piping, a couple fans, and several vents.

To start, it must remove the hot air from your house. It draws it out using a simple network of fans and ducts.

Then, it needs to replace the hot air with cold air. For that, it has to enact the miracle of cooling down the refrigerant.

It starts by compressing the refrigerant into a small volume. Due to the Ideal Gas Law, this warms the refrigerant up. It circulates through your outdoor unit, which uses the ambient air temperature and fans to cool it down.

Then, the cool, condensed refrigerant is sent inside your house in small pipes, coiled up to keep it as compressed as possible. Finally, it’s thrown into much larger chamber, where it quickly expands and, because of the Ideal Gas Law, cools down even further.

Inside this chamber is another pipe. That pipe contains air from your house, which was sucked in by an intake vent. As the warm air from your house passes through the pipe in the chamber, it’s cooled down. Then, it’s sent out of vents into your house, giving you that sweet, cold feeling you love.

How Your AC Keeps Your Air Clean

Your AC doesn’t just cool your house. It also keeps the air in your house free of allergens, pollution, and contaminants.

Every time you open a door or window, you let in outside air. This air is chock-full of pollen, dust, pollution, and particles. Over time, without your AC system, you would notice your air becoming significantly dirtier. This can cause health issues and overall breathing difficulty.


Your AC system combats this with the air filters in the intake vents around your house. When dust and particles try to enter your AC system, the filter catches it. This prevents dirty air from damaging the system and being ejected back into your home.

Your filters are extremely important to your health and the health of your system. It should be changed every three months. If you have a pet or live in a particularly dusty area, it should be more frequent.

Filter King specializes in providing the best quality air filters for the best prices. We even offer subscriptions for air filters to be automatically delivered to your house whenever they need to be replaced. You’ll never forget a replacement again!