How Do Window Air Conditioners Work?

Window air conditioners can be a life saver in the summer months. Over here in Kansas we routinely get temperatures over one-hundred degrees in the July and August months. On some particular bad summers we may get one, two, or even three weeks straight of one-hundred temperatures. Don’t worry though at night it goes down to a balmy eighty-five degrees for the low. This is NOT good sleeping weather!

Most of us escape this heat by having our central air systems working off the clock. But, how do people escape the heat when their home doesn’t have a central air system? Some of the older homes out there from the sixties, fifties, and even older just did not come outfitted with a central air conditioning system. At the time their house was built the technology was still so new and expensive that a lot of builders and home-buyers couldn’t afford it. In 2018 our summer will be hotter then ever thanks to the lovely effects of Global Warming. So, how, do people living in these houses or people living in apartment complexes escape the heat?

Friedrich Chill CP06G10B 6000 BTU Window Air Conditioner
Friedrich CP06G10B Window AC

The answer for so many people are window air conditioners. They provide even the person who is in the most dire of circumstances the option to cool their home or apartment. I am a huge advocate of these machines for that reason and that reason alone. A cheaper model unit will only cost you between one-hundred and two-hundred dollars.

Check out current prices on Amazon

Most people can save that amount of money in a short amount of time if they really want to get out of the heat.

How Do They Work?

As I said up above window air conditioners are found nearly everywhere in the United States, but how do they work? Through out my research on these products I came across a lot of mis-information and some notions that were just flat out wrong. One of them was someone asking if they could get carbon monoxide poisoning from a window air conditioner. The answer is no! Another one of these questions that I saw over and over again was can I install the window unit by just having it sit on my kitchen table? After you finish reading this article you will be able to understand my frustration here. The heat of the room has to go somewhere. There has to be an exhaust. If the heat can’t go anywhere then your air conditioner isn’t going to be accomplishing anything.

Split System Versus a Window Unit

Window units work exactly the same as a split system and they have the exact same kind of components. For those of you who don’t know a split system is your traditional home air conditioner that you find in newer homes complete with intake and outtake ducts. These are the units that sit outside your home and have the large fan going round and round when it’s kicked on.

The only difference is that a split system is just that, it is split. That means that the components are in two different locations. One of them, and the one you are most likely familiar with, is the outside air conditioning unit. This unit contains your compressor, your condenser, and your fan. The other section of your central air conditioning system is usually located above your furnace. Here you will find your evaporator, your blower, and your air filter.

I will get into exactly what these components do and how they interact with each other in just a moment. Firstly though let’s finish looking at the differences between the window and split units. A window unit has all of the components we mentioned above all packed into one box. On top of that the window unit is designed to cool only one room, maybe two. While a split system is designed to cool an entire home. If you are going the window air conditioner route for your entire home then you will need to buy multiple units for various rooms so that you can ensure your house stays cool.

How They Work

Ok folks, so now we know that a window unit and a central air, or split system, work in the same fashion. The only real main differences are their size and where the components are located.  Now lets get into the real science on how they work and how they cool your home.

Refrigerant Cycle in a Closed System
Example of a Refrigerant Cycle in a Closed System

First and foremost let me tell you that your home air conditioner does not produce ‘cold air,’ in the same way that your furnace would produce heat. With a gas furnace you have the heat from the flame blowing into your home. Instead of that air-conditioners are all about transferring heat and changing states of the refrigerant.

The refrigerant is used to absorb the heat from inside your home, carry that heat to your air-conditioner, and then release it to the outdoors. Once the heat has been removed the colder air blows back into your home. The refrigerant circulates continuously to remove additional heat from your home until your desired temperature is reached.

In order for a refrigerant to absorb heat a change of state has to happen. When I say change of state I am talking about going from liquid to gas and from gas to liquid. It is important to remember that the refrigerant cycle is just that, a cycle. That means that it goes over and over again. There is never any break to this cycle and should never be any leak in this cycle. It is a completely sealed process. Within this cycle there are different components that allow for the refrigerant to change pressure, temperature, and state. We will go over these as well as the process of the refrigeration system.

The Process & Components

Home AC Cycle – Picture Credit from ConsumerReports.Org

The picture above is a great illustration showing you how everything is laid out for a home air-conditioner. That being said, I will say that it does not label the components in order of process. But, that’s OK I will do that below for you. If you are unsure of what component I am referring to please consult the picture above to get an idea. Yes, I realize that this is a picture of a split system but as we have already covered a window air conditioner works the VERY same way. The only difference is arrangement of components. (I also didn’t have a picture of inside a window air conditioner readily available.)

  1. Evaporator – The evaporator’s cooling coils remove the heat and humidity from the air inside your home using the designated refrigerant. Ever notice when your air conditioner kicks on and doors that were slightly ajar get ‘sucked’ close? That is your system pulling out hot air from your home.
  2. Suction Line – This is where the refrigerant is ‘sucked’ into the compressor. This is also known as the low pressure side.
  3. Compressor – The compressor is a pump that moves the refrigerant between the evaporator and the condenser to chill the indoor air. The compressor is often seen as the heart of the system. Instead of pumping and metering the blood flow to the rest of your body it pumps and meters the amount of refrigerant to the rest of the system. Upon entering the compressor the refrigerant is in a vapor state and as it’s name suggests the compressor’s job is to compress the vapor. When a vapor is compressed both the pressure and temperature of that vapor increases. The vapor leaving the compressor is VERY hot as a high temperature and high pressure vapor.
  4. Discharge Line – The high temperature vapor refrigerant then moves it’s way through the discharge line and into the condenser.
  5. Condenser – Upon entering the condenser the high temperature refrigerant air from a fan passes over the coil to cool the vapor refrigerant. As the vapor cools it undergoes a state change and changes into a liquid. At this point is where the hot air from inside your home is removed as the fan blows the air over the coils and outside of your home. If you ever stuck your hand over the top of your air-conditioner you would feel the hot air being blown out. That is your condenser at work.
    1. While in the condenser the refrigerant will begin to turn into a saturated state. A saturated state is where vapor and liquid both exist at the same time. The saturated state is where the majority of the energy is transferred. This is where the heat that the refrigerant is carrying is dissipated. At this point the refrigerant begins to absorb the heat and as it does it moves to liquid.
  6. Liquid Line – The high pressure liquid refrigerant moves it’s way through the liquid line and into the metering device. This point of the cycle is known as the ‘Subcool’. If there is a problem with your system this is where most technicians start looking.
  7. Metering Device – The metering device’s purpose is to control the amount of liquid refrigerant that will be fed into the evaporator. Inside the metering device is a dividing point between high pressure and low pressure sides of the system. As the refrigerant is passed through the metering device the pressure drops.
  8. Evaporator Again – After leaving the metering device the low pressure liquid refrigerant immediately moves into the coils of your evaporator. Just like with the condenser the evaporator has a fan blowing against it’s coils. But this time instead of blowing hot air out of your home it is now blowing the cold air back into your home. Here is where big state change happens.
    1. As the refrigerant enters the coil at a lower pressure it begins to bubble and boil and as it does it begins to change state back into a vapor. (Same concept as boiling a pot of water and watching it all evaporate.) During this process of changing state from liquid to vapor the refrigerant is removing energy, or heat, from the air passing over the coils. The heat that was in the air is transferred into the refrigerant. Remember, it’s not about creating cold air but about removing the heat. Since the heat has been removed from the air when the fan blows over the evaporator’s coils cold air will blow into your home.
  9. Repeat – After this the whole process is started over again and again until your home has reached the desired temperature set on your thermostat.


Ok folks, are you confused yet? No worries. It is a hard concept to grasp. It’s actually almost one of those things that you have to review and review in your head until it finally clicks. Once it does click it all makes sense you begin to wonder why you didn’t know it before hand. Just remember that air conditioning or refrigeration all follow through relatively the same cycle. It’s all about changing states and absorbing heat.

I hope this guide was helpful folks and I also hope that you learned a little something. If you are interested in purchasing a window air conditioner then I would highly suggest that you visit our Window Air Conditioner Buyer’s Guide by clicking this link. This article goes through every consideration and little thing that you need to consider before purchasing a window unit. It also goes into recommended products for each room size in your home.

Thanks for reading, and stay cool out there my friends!