How Do Window Air Conditioners Work: (Explained with Images)

Suppose your home doesn’t have a central air conditioner, or you need only to cool a specific area. In that case, a portable air conditioner might work, but a window air conditioner definitely will. Window air conditioners are powerful, semi-permanent, and easy to use.

This article will examine window air conditioners to give you all the information you need. Whether you are looking to understand how they work, looking to make a purchase, or just want to compare them to other AC types, we have you covered.

A Brief History Of The Window AC

The theory of air conditioning has been around since the late 1800s. Commercial units were developed and used in theaters and auditoriums as early as 1905. However, costs, production, and shipping hindered the industry for a while.

Automotive refrigeration was a step in advanced technologies that helped develop the country and ship produce and meats to and from regions all over the States. In 1931, though Schultz and Sherman took portable air conditioning to a whole new level.

While their window unit was compact, decently powerful, and could cool large rooms, the $10,000+ price tag kept it out of reach for most people. After World War II, though, that all changed.

As prices plummeted, more sales were made, and production increased. Until central air conditioning also began to gain popularity, the window units we know today were the answer to a lot of hot summer prayers.

How Do Window AC Work

How Window Air Conditioners Work

Window air conditioners work very similarly to portable air conditioners and even central air conditioners in how they work. In essence, they take air from the room and outside, cool it down, and send it into the home to lower the temperature.

It all starts with the intake. Once you turn the unit on, fans begin to spin, bringing air in through the intake vents. Part of this air passes through the condenser coils, which pulls the heat from the refrigerant as the air passes back to the outside.The rest of the air passes over the evaporator coils, where the heat is pulled from the air and absorbed by the refrigerant. Humidity and moisture condensate on the coils and drip to the collection tray.

As the cold air enters the room or home, the condensate exits the window AC through the drain hole or gets evaporated and carried back outside. Meanwhile, the hot refrigerant gas in the cooler coils is sent through the condenser coils.

Here, the heat is removed, and the refrigerant cools slightly, allowing it to handle compression. As the refrigerant enters the compressor, it is pressed into a high-heat liquid with high pressure.

This pressure is compound in the capillary tube where the refrigerant slows to make it through the much smaller hole. If there is an expansion valve, the refrigerant also passes through this.

Either the tube or the valve (or both) removes the heat from the liquid and begin the process of expanding to a gas. The cold gas enters the evaporator coils, where the entire process begins again.

Standard Parts of a Window Air Conditioner

Almost all air conditioner types run off of the same concepts and principles. Thermal Dynamics are the laws that all heat exchange and cooling systems utilize. Though the various parts and interactions can change a bit, the main components of window air conditioners are listed here.

AC Compressor

The compressor is responsible for taking the cold, expanded refrigerant gas and compressing it into a hot, high-pressure liquid.

The pressure forces the refrigerant through the system, where it cools, expands, heats, and cycles through.

You can think of the compressor as the heart of the refrigeration system.

Condenser Coils
AC Condenser Coil

The condenser coils take the heated refrigerant gas from the evaporator coils and allow it to cool. The fans bring air in and blow them over the coils until the refrigerant inside is cooled. From here, the cold gas is sent to the compressor, where it is pressurized and turned back into a liquid.

Cooler Coil

The cooler coils, also known as the evaporation coils, are the coils that take the cold refrigerant liquid and expand it into a gas. This reaction causes a heat exchange that removes the heat from the air passing over the coil. The cold air is then sent into the room by the fans, and the hot gas is moved on to the condenser coils.

AC Capillary Tube

Capillary Tube

In smaller refrigeration systems, the hot liquid refrigerant doesn’t have the space or time to begin thermal expansion with just an expansion valve alone.

A capillary tube is used to slow the refrigerant down and jump-start the expansion system from a high heat liquid into a hot gas.

Fan Motor
AC Fan Motor

The fan motor is responsible for spinning the fan and blower that bring air in and exhaust air out of the system.

Without a fan motor, the system would run, but it would soon overheat, and no cold air would enter your home.

Propeller Fan/Blower
AC Fan Blower

The blower fan is the small fan responsible for taking the intake air and passing it over the cooler coils.

Once the air is cold, the blower fan then moves the air through the air vents and out into the room.

The air lowers the room’s temperature or space, and the cycle repeats until the room is at the desired temperature.

Operation Panel
AC Operation Panel

The operation panel will vary from model to model. Some will be all turn dials and toggle switches, while others will be digital.

The options are generally the same, though, depending on features.

You will have the ability to turn the unit on, adjust speed and cooling modes, set timers, adjust the temperature, or enable vent and louver oscillation.

Filter Drier
AC Filter Drier

The filter drier is a critical part of most AC systems. This is a small filter that is generally installed after the compressor and before the expansion valve. It will remove any moisture or contaminants from the refrigerant.

It also holds a secondary purpose of removing physical contaminants. However, through a sealed system, it may never become completely full or blocked and may or may not ever require replacement.

AC Air Filter

Air Filter

The air filter on a window unit is generally a screen filter. It is designed to keep the fans and air entering the room cleaner.

Dust, debris, and larger particles are collected. However, only a few models use paper or HEPA quality filters in their machines.

Drain Pan

The drain pan is a piece that is not exclusive to window units. You will find a drain pan in the evaporator unit in central air units. On window models, the drain pan is generally the entire bottom section of the machine.

The drain pan collects the condensate and moisture from the cooler coils and either holds it so it can evaporate or sends it through a drain line outside of the system. On a window unit, the drain line may be as simple as a small rubber hose that drains outside the window or just an angled pan with a hole in the corner.

Temperature Control/Thermostat

Part of the control panel adjusts the temperature. Using this setting is the same as using the thermostat on your home’s central AC system (if you have one). The control adjusts the internal thermostat that tells the system to turn on or off.

Depending on the temperature you select, the thermostatic controls will activate the system when the ambient temperature becomes too high and shuts it down when the temp drops low enough.

Common Features Found in Window AC Units

Several features are found on window units that may or may not always be present on other air conditioner types. The following list isn’t essential to cooling operation, but they make it easier to control, use, or enjoy.


A timer function can work in a couple of ways. The primary method is an automatic shut off of the system. You can select the time to run (usually 1, 2, 4, 6, and 8 hours), and after the time is reached, the system will shut down.

Other models have automatic timers to turn on or off and work as an alarm clock, coming on at a particular time and shutting down at a certain time. These are great energy savers since you can program them to only run when you are home.


Remote operation is almost standard in modern machines, but the infrared remotes still work from only about 30 feet away. Smart window ACs can utilize mobile apps, allowing you full control even when you aren’t home.


Fan mode is an energy-saving mode that doesn’t cool the air but keeps air flowing. With the fan on only, you can’t adjust the temperature, but you can adjust fan speed or even use a timer. If you want air circulation but don’t need to cool the air, fan mode is a great place to start.


Auto mode allows the system to take sensor readings on humidity levels, ambient temperatures, and other factors. Based on the readings, the system will choose the best speed and operation mode to run at the most efficient settings for the temperature set.


A secondary feature of air conditioning is natural dehumidifying. The warm, humid air is cooled, and the moisture is condensed on the evaporator coils. You can also run some models in dehumidifier mode, where there is little to no output, but the system cycles the room’s air by removing the moisture.


Some brands and individual models will feature automatic tilting louvers. They can rotate, move up and down or left and right. This changes the direction the air is released into the home, just like an oscillating fan.

Window Vs. Other Types of Air Conditioners

How do window air conditioners stack up against other AC types? Let’s take a closer look.

Window AC Vs Other Types

Central AC Units

Central air conditioners are a permanent install that generally uses a split system. The condenser unit outside holds the compressor and condenser coils. It is also where you will find the filter drier.

Inside the evaporator unit is usually found in a closet, attic, or false ceiling. The blower fan is connected to a series of ducts that send the cold air out to the various rooms through the room vents.

Unlike a window unit, a central AC will cool an entire home. However, the initial costs can easily reach over $1000 for the installation, and even Energy Star rated units will cost more to run than a window unit.

Related Article How Does A Central AC Work?

Mini Split AC Systems

Mini Split systems use two parts, including the internal evaporator and fan unit and the external heat pump. The heat pump is a special compressor that runs in both directions. This allows the system to take heat from the house and push it outside like a central unit or reverse direction.

In the reverse direction, the pump takes heat from outside and pushes it into the home. Mini-split systems are highly efficient, often reaching 22 SEER ratings or higher. However, they are a bit more limited than a central system.

Ducted mini splits are usually found as replacements for older central air systems, using the same ducting and room vents. A ductless system is cheaper, but like a window AC, it will only cool (or heat) a room where an internal fan unit is mounted.

Portable AC

Portable air conditioners are very similar to window units. They also only cool a single room or a couple of connected rooms. Instead of the entire unit mounting to the window, though, only vent hoses are mounted and held in place by the window frame.

The rest of the unit sits on wheels in the room, where it can be positioned or moved as needed. Generally (though not always), a window AC is more powerful and capable than a portable AC unit. Though, the difference is that if you need to cool another room, a portable unit is much easier to move and maintain.

Related Article How Does A Portable AC Work?

Window Mounted Vs. Through The Wall

Window units and Through-the-Wall air conditioners are virtually identical. There are a few small differences to be aware of, though.

The first thing to note is how they are mounted. Through the wall units require a hole cut to size all the way through the wall of your home. The hole is filled with a mounting cage that the AC will slide into. It is a more permanent mounting, which can leave your home open to drafts or external air when the system is not in use.

Through-the-Wall models also tend to have drain lines installed on the drip trays. This ensures the water collected is drained outside and doesn’t sit in the cage where it can rust or even run into the home.

You should also note that while a window unit can slide into a through-the-wall cage and work just fine, it is much more difficult (and ill-advised) to use a through-the-wall air conditioner mounted in a window. It can cause damage, fall out, or break the window sill if not mounted into a cage.

Keeping Window ACs in Tip Top Condition

To keep your window air conditioning unit running in top condition, prolonging life expectancy, and making the unit more efficient, there are a few things you can do.

  • Start the AC before the room heats up.
    It is easier to keep a room cool than to cool a hot room.
  • Don’t run the AC when you aren’t home.
    Use the timer or mobile app to stop the AC after you leave the house or turn it on just before you arrive home.
  • Use floor and ceiling fans.
    Air circulation and distribution will help the window unit be more effective. It will also run less, making it more efficient.
  • Clean on schedule.
    Ensure the drip tray is clean, the filter is washed or replaced, and intake as well as exhaust vents are free from dust, debris, and build up.

People Also Ask (FAQ)

What is the standard size of a window air conditioner?

You can find window air conditioners in a wide variety of sizes to accommodate most single and double-hung windows. However, the industry average is designed to fit most residential homes. This means the units are made for double-hung windows with a width of 26 to 32 inches and a height of at least 15 inches.

Do you have to vent a window air conditioner?

There isn’t any extra venting needed when the unit is installed correctly. The rear vents of a window AC unit force hot air outside and draw in fresh air when needed. Because it sits on the window sill, the rear intake and exhaust vents are already vented outside, so no further action, setup, or installation is required.

How do you install an air conditioner in a window?

Window AC installation is easy enough for a single person. However, some models can weigh quite a lot and be awkwardly sized. It is always best to have two people to lift and mount the air conditioner. First, you will open the window and remove the screen.

Ensure the power cord is on the inside part of the window and clear of the AC, set the AC on the window sill from the inside of the house, and position it back until the bottom lip catches on the window pane rail. Holding the AC level, bring the window pane down, so the top lip of the AC is on the inside of the pane frame.

If there are gaps on the sides, you can use the included accordion shutters. They will screw into the casing of the AC and stretch to the inside of the window frame. You can screw the panels to the window frame or use double-sided adhesive to hold it in place. Then, plug the AC in, and you are ready to go.

Do window air conditioners pull hot air from outside?

No. The intake and exhaust fans are separate, and the internal components are in a sealed system. The exhaust air is vented outside, but fresh air is never pulled in from outside the home.

What does the fan mode do on a window air conditioner?

Fan mode keeps the compressor off and just cycles air from the room back into the room. This process helps keep airflow and circulation going without relying on the AC to cool the air or waste energy when the air conditioner isn’t needed, but air movement is.

How to tell if window AC is working or not?

You can tell if the air conditioner is working or not through several methods. The most obvious is to feel the air coming from the vent. If the unit is on and all indicators are normal, but the air is warm, hot, or just not as cold as it should be, it can mean there is a problem.

Most issues can be solved by either resetting the system or cleaning the filter. Airflow is the leading cause of cool but not cold air coming from an AC. Unplug the unit from the wall, remove the air filter, clean it off, and put it back. By the time you are finished cleaning, the air conditioner will have reset.

Once you reinstall the air filter and plug it back in, your system should be working. If it is not, it can mean a problem with the compressor, which needs a trained repairman or HVAC technician to diagnose or repair.

How else can I help cool a room when using a window AC?

To help the window air conditioner keep a room cool, there are steps you can take. First, ensure that the room is closed off from external air and heat sources. Shut the doors and close windows to keep hot air outside. Close curtains and keep the window unit from running while in direct sunlight.

You can also utilize floor or ceiling fans to help air movement in the room. You will also want to ensure you don’t install the AC near any internal heat sources like televisions, refrigerators, or radiant heaters.

What are the best window air conditioner brands?

There are several well know, trusted, and top-rated brands. Names like LG, Kenmore, Frigidaire, Friedrich, Haier, and GE are at the top of almost every list.


Window air conditioners are compact, easy-to-use room air conditioner systems that are generally energy-efficient and affordable. This guide gave you the information you need to understand the AC type and learn if it is the correct solution for your needs.

While there are several types of small or compact air conditioners, window units are among the most popular and easiest to install, making them ideal for permanent or temporary use.

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Josh Mitchell


Josh Mitchell
My name is Josh and I am obsessed with home appliances. From portable AC units to heaters and air purifiers, I enjoy testing, learning and using these devices to improve the air quality inside my family home.

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