Are you wondering ‘How do window air conditioners work?’

While these devices may seem complicated, the process behind how window AC works to cool the air is actually quite easy to understand.

In this post, we’ll explain everything you’d ever want to know about how does a window air conditioner work.

The areas we’ll cover include:

  • The Room Air Cycle
  • The Hot Air Cycle
  • What The Thermostat Does
  • Controlling Air Speed
  • Function of the Air Filters

After you’re done reading, check out our free guide on the best window AC unit where we show you what features to look for to find the perfect AC unit for your own home.

Also, this same information applies to through the wall air conditioners which are basically the same thing as window AC units. The major difference is that you can install them inside a wall as a way to free up your window.

To find out more about those options, take a look at our guide on the best wall mounted air conditioner.

How Does a Window Air Conditioner Work?

How does a window air conditioner work

Window air conditioners are installed in an window and it uses two air cycles. The interior of the unit uses a fan to blow air over the evaporator to cool the room. The exterior of the window unit uses a second fan to blow outside air over the condenser to cool it down.

The Room Air Cycle

The whole point of a window air conditioner is to get the air moving.

The air inside your room, out in the front of the air conditioner where the cooling coil is, that’s what we call “room air.”

Once the window AC kicks in, its blower starts up, followed by the compressor. The cooling coil (or evaporating coil) starts to drop in temperature as soon as its compressor starts.

The blower pulls in room air that’s hot and full of dust particles and moves it through the air filter, separating out the unwanted particles.

Next, the air passes over your cooling coil.

Two things happen here:

First, given that the coil’s temperature is much lower than the room air, the coil absorbs the heat; this causes the room’s ambient to drop; “chilling” the air.

Second, the cooling coil’s temperature is lower than the room’s dew point, causing (you guessed it) dew to form on the cooling coil’s surface.

This removes moisture out of the air, dropping its relative humidity values.

This low-temperature, low-humidity air is sucked in by the AC’s blower, and “exhaled” at high velocity, passing through a metal duct, and blown out through the AC’s front panel.

This pushes air into the room and chills it, keeping temperature and humidity levels low.

Of course, it doesn’t stay that way.

The room’s air has higher moisture and temperature levels than the chilled air, transferring those properties to the new air.

That means it gets sucked in again by the blower and the whole cycle repeats.

The Hot Air Cycle

Another important aspect of understanding how do window AC units work is the hot air cycle.

This cycle focuses primarily on the external, or “atmospheric” air used to cool the condenser.

So what’s the condenser?

The condenser is the part of the AC that’s outside the room.

It’s exposed to your external atmosphere, and the condenser’s propeller fan sucks in the high-temperature atmosphere and blows that air right over the condenser.

The condenser itself contains refrigerant, but it’s at a high temperature.

It needs to be cooled before it provides cooling.

The “atmospheric” air is already comparatively hot; after absorbing the condenser’s heat, the temperature rises even higher.

Stand behind a window AC some time and see for yourself; it’s hot back there.

All this hot air is how the cycle gets its name.

Once it’s cooled, the refrigerant first enters into the expansion valve, and then the evaporator, or cooling coil.

The hot air blends with the atmosphere and the fresh atmospheric air gets absorbed and pushed over the condenser.

Thus continuing the cycle of hot air.

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What’s the Thermostat Do?

This is another key factor in understanding how does a window air conditioner work.

Every air conditioner possesses a thermostat, even the small room coolers.

Inexpensive products cut costs by using a rotary dial, while the moderate to higher-priced AC units for windows include digital controls.

No matter how you set it, you enter a desired temperature equilibrium for the room.

Once the thermostat detects that you’ve reached your desired temperature, it halts the compressor, and the cycles cease.

However, once the room’s ambient temperature rises once more, the thermostat removes its hold, kicking the compressor back into gear, and getting the cycle going.

With that in mind, setting your thermostat lower isn’t going to cool things any faster.

It’s just a setting that tells the unit when it’s time to shut off.

Adjusting Air Speed

The blower fan, on the other hand, has a speed that you can set.

There’s nothing too fancy here.

It’s simply a fan. Setting it faster means that air will cycle through the room more quickly, which can speed up the cooling process.

It’s also nice to stand in front of if you’re roasting in a hot room.

The Function of Air Filters

At the beginning of this article, we mentioned how the blower pulls in room air and along with it comes dust particles.

Fortunately, window AC units come with an air filter that catches all of that.

It’s vital to clean these every few weeks or so.

Skip this part, and the filter gets clogged.

Clogged filters mean that dirt starts getting into your evaporator coil, choking it.

Once this occurs, the AC device will stop functioning and you’ll either have to pay for the evaporator coil to be cleaned by a professional or replace the entire unit with a new one.

Cleaning the air filter only takes a few minutes worth of work and it’s worth every second.

Maintain it regularly, and your window air conditioner will provide blissful cooling for years to come.

Summary for How Do Window Air Conditioners Work

We hope you enjoyed this guide on how does a window air conditioner work.

As you discovered, window AC units use two air cycles to cool down a room and the unit itself.

Another important aspect for how do window air AC units work, is the thermostat. Without this key element, the air conditioning unit could not regulate the temperature inside a room.

Air filters are also an essential component of window air conditioners to keep them operating and working effectively to chill the space.

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About David Morrison

David is an Air Quality & Comfort Technician. He has expert knowledge on the technology and design of air purification, air conditioning, and heating systems. His main role is to write content that helps people get the most value out of their air purifiers, air conditioners, and heating units. (See Full Bio)