How Does An Air Conditioner Work

How Does An Air Conditioner Work

It’s a gross summer and you’re stuck working remotely from your overheated apartment. You bought the previous tenant’s window unit air conditioner, but when you turn the unit on it grumbles and sputters and doesn’t blow any cool air. Well, you’ve always been handy, good at tinkering. So you pop the front off the AC unit and look inside, only to be confronted by filters and fans, compressors and condensers, and the realization that you have no idea how an air conditioner works.

You’re not alone. Knowing how an air conditioner works will keep you cooler and save you money, so it’s worth learning the basics. We’ll go over the mechanics behind your AC, as well as some general knowledge about your cooling system. While you might not be an HVAC pro, you’ll be able to answer the next time someone asks, “How does AC work?”

So, how does an air conditioner work? Well, very broadly, your AC takes hot air, pulls the heat out, throws the heat out the window and blows the newly cooled air around your home. A common myth about how an air conditioner works is that it pulls in outside air. However, most modern air conditioners, and every window AC, uses only indoor air.

Have you ever seen the exhaust coming out the back of a window unit? That exhaust is the byproduct of the AC process and actually holds the heat your AC extracted from the air. That sounds a bit complicated, so let’s go into more detail on how the parts of your AC works.

The key cog in your air conditioner isn’t mechanical, but chemical. That chemical—the Refrigerant—constantly changes between a liquid and a gas. When people hear refrigerant, they tend to think of Freon, which is highly toxic and damaging to the environment. However, production of Freon was phased out starting in the 1990s. Modern refrigerants are still toxic, so if you ever think the refrigerant is leaking in your AC, contact a professional!

Okay, so we have the Refrigerant—but how does an air conditioner work with the refrigerant? There are three primary mechanical components to your AC: the Evaporator Coil, the Compressor, and the Condenser Coil. When you turn on your AC, it uses its fan to draw warm air over the evaporator coil. Inside the evaporator coil is the refrigerant, which heats up and evaporates. The compressor directs the evaporated refrigerant through the AC, applying pressure to the vapor, which in turns heats the vapor up. The hot, evaporated refrigerant reaches the condenser coil, where two magic things happen. First, the pressure on the refrigerant turns the vapor back into a liquid. Second, in the process of becoming a liquid, all of the refrigerant’s gathered heat jumps ship. 

As your high school physics teacher (and Isaac Newton) said, heat always travels to a cooler area. In the evaporator coil, the heat moves from the air into the refrigerant, because the refrigerant is cooler. Now the opposite happens: the refrigerant sheds all of the heat it has absorbed. The heat leaves the air conditioner via its exhaust vents, the liquid refrigerant returns to the evaporator coil, ready to pick up more heat and begin the process again. 


Okay, but how does an AC work with humidity? Humidity, besides being an unpleasant atmospheric condition, refers to the amount of water vapor in the air. As air gets warmer, it can hold more water vapor, which is why warm days feel more humid than cool days. This principle also applies to the air in your home: as your home heats up, the indoor air tends to grow more humid. By pulling the warm air out of circulation, extracting the moisture, and recirculating cool air, your AC fights against that humidity. Remember the exhaust we discussed earlier? That’s basically your home’s humidity. On some days, you can see moisture dripping from the exhaust of an AC. This “urban drip” is—you guessed it—even more humidity. A side note: no one likes when an AC drips on them, but urban drip is not harmful, just unpleasant.


There’s another, glibber answer to the question, “How does an air conditioner work?” And that answer is, of course, “You plug it in and turn it on.” But there’s a well, actually response to even that joke. Understanding this seemingly pedantic point can save you money and help the environment.

First, let’s go over some quick electric bill math. In most places, your electric bill is rated in kWh, which stands for kilowatt-hours. Air conditioners, like all appliances, have a plate installed with information including their power consumption. This information might be provided in Watts (abbreviated W), or broken down into an Amperage (abbreviated A) at a Voltage (abbreviated V). For example, the Windmill Air Conditioner averages a power consumption of 690W, which is equivalent to 6A at 115V. 

Let’s say you ran your Windmill AC for 6 hours today. At 690W of consumption, that’s equivalent to 4.14kWh. The average US electric bill is a bit over 13¢, so let’s round up to 14 (because we know the utility company definitely will). At 14¢ per kWh, running your AC today cost you about 58¢. If we ran the AC for 6 hours a day for 30 days, the cost would be about $17.39.

Our reward for solving this math problem is we now have an idea of how much our AC costs to operate normally. While you won’t receive an itemized electric bill, you can still use your electric bill as a diagnostic tool for your AC. Huge spikes in your electric bill can signal a number of problems with your AC or its installation. 

Before you check the terms of your warranty, there are a few easy ways to make sure your AC is set up how an air conditioner works best. The first thing to check is the filter on your unit, as a clogged filter lowers the unit’s efficiency. For more information on filters, check our article on that subject. The next check is insulation. Remember how we said that warm air moves to a cooler area? If your AC is installed without insulation, or with gaps in the insulation, warm air will come in through the openings. This will—you guessed it—make your AC run longer and work harder to keep your room cool.

There are also some technical issues which can contribute to energy bill spikes. Internal components like compressors tend to consume more energy as they age, so older units will cost more to run than newer models. It’s also possible that your unit is wrong for your living space. We have an article that goes into more depth on that subject (including explaining what a BTU is) if you’re curious. The tl;dr is that different machines are intended to work in different sized areas. Using a unit that’s too strong for a small room will cause the unit to cycle off quickly, wasting electricity and never dehumidifying a space. Too few BTUs and the unit will run forever, cooling nothing. 


The internal mechanisms of your air conditioner might be complicated, but the theory is straight forward. Your AC doesn’t make cool air, it takes the heat out of the air in your home. Air loses heat and cools down as it passes over the evaporator coil, just like how the refrigerant loses heat in the condenser coil. Remember to check common issues like your filter and installation if you notice issues with your unit’s performance. It’s also a good idea to keep an eye on your electric bill so you can see if there are any spikes in power consumption. Now that you know how your unit works, you can check out this article for tips on keeping your AC in tip-top shape. If you want to know more about choosing the right AC unit for your home, check out our article on that subject. And as always, if you ever have any questions about your Windmill AC, our support staff are available to answer questions every day of the week.