How Does a Window Air Conditioner Work?

Not to scare you out but there are numerous studies that link extreme heat with breathing problems, exhaustion, or even heart problems. While most people are using central air conditioning systems to tackle this problem, this isn’t always the most affordable option. This is why we want to draw attention to other functional yet overlooked coolers — window air conditioners.

But how does a window air conditioner work and why consider buying one are the questions that you are probably asking yourself now. Let’s discover.

Parts of a Window Air Conditioner That Cool Your Living Space

In order for you to understand the way window air conditioners work, it is crucial to know the parts inside them.


Known as the heart of an air conditioning system, the compressor serves as a pump that basically moves the refrigerant between the evaporator coil and condenser coil.

Fan & Blower

These two highly important parts of a window air conditioner perform two different functions. While the main function of the fan is to suck in warm air from your room and release it outside, the blower discharges cool air into your living space by circulating hot air over the evaporator.

Condenser Coils

These coils are typically located in the back of the unit and their main function is to collect your indoors heat that the fan has sucked in and reject it outside.

Evaporator Coils

Located near the air handler, the evaporated coil absorbs indoor heat and humidity from the air and removes it using a refrigerant.


The main function of an air conditioning filter is to trap pollutants such as mold, dust, fungal spores, and pet dander that the air in your living space contains. If the filter isn’t cleaned or replaced in a timely manner, it might hinder the airflow — which could harm your indoor air or increase your power bill.


Thermostats control the temperature of your room, turning on the window air conditioner to cool down a hot room or vice versa.

Expansion Valve

Working on the throttling principle, the main function of the expansion valve is to bring down your air temperature. This part of your window air conditioner is located between the evaporator coils and condenser coils.

Chemical Refrigerant

In a nutshell, refrigerant is a substance that absorbs heat from your living space, transitioning from a low-pressure gas to a high-pressure liquid.

The science behind this is as follows: the compressor moves the refrigerant as a low-pressure gas while pushing the gas molecules together and, as the pressure rises, it heats them up. Then it pumps this gas into the condenser which uses fans to cool down the gas, pulling the molecules closer together. This allows the refrigerant to condensate into a low-pressure liquid that cools down the temperature in your home as it moves through the evaporator.

Room Air Cycle

The room air cycle showcases the way these parts work together to create a cool and airy atmosphere in your home, using the air from your living space.

The thermostat in your window unit detects that the temperature levels increase during hot summer days which triggers the following actions:

  • The process begins as the blower sucks in warm air and circulates it over the evaporator.
  • The second thing that happens is the compressor turning on automatically, enabling the refrigerant to move through the evaporating coil.
  • Before the air goes any further, it moves through the filter which traps all the airborne particles.
  • Once the air is free of any pollutants, it passes over the cooling coil, which, thanks to the refrigerant flowing through it, is naturally at a low temperature. This allows for heat absorption, lowering the temperature in your living space.
  • This happens as the unit quickly blows the now-cold air back into your room, which mixes with the warm, humid air and cools it down. This significantly lowers the humidity in your room as colder air can not hold as much moisture as warm air does.

Hot Air Cycle Important Parts & the Way It Works

Important Parts

Expansion Valve

The expansion valve allows phase transition from a liquid to vapor in the evaporator by removing pressure from the liquid refrigerant.


It is part of the window air conditioner which rests outside, containing a propeller fan that sucks in warm air and releases it outside through the condenser itself.


Running completely different from the condenser, the evaporator converts refrigerant liquid into a gas by absorbing heat from the air in the compartment.

The Way It Works

The hot air cycle works opposite from the room air cycle as it uses external air to cool a part of the window air conditioner located on a unit section that rests outside — the condenser. This is done as the propeller fan in the condenser sucks in hot air and moves its molecules over the surface of the condensing coil.

The condenser contains a high-temperature refrigerant that needs cooling before it begins to bring down the room temperature. As it reaches the unit, this refrigerant is quite hot, with the condenser coil making it even hotter.

Fun fact: this hot air is how the entire cycle gets its name.

After passing through the condenser coils, the refrigerant (which is now in a gas state) penetrates the expansion valve which removes some of the pressure and heat. As a consequence, the air causes it to become liquid at a cooler temperature, automatically cooling the condenser.

The refrigerant then continues towards the evaporator which completely removes the heat, enabling this cooled atmospheric air to be discharged outside. This is how a completely new atmospheric air enters the window air conditioner, thus continuing the cycle.

How to Increase the Efficiency of Your Window Air Conditioner?

There are a few simple things you can do to increase the efficiency of your window air conditioner which include cleaning the filters and coils and giving it a rest.

Clean the Filters

Cleaning the filter in your window air conditioner is the most important thing you can do to boost its efficiency. This is mostly because it traps airborne particles on a daily basis which might affect its efficiency if not cleaned regularly. The recommended time to clean this highly important part of your unit is once a month.

Clean the Coils

It’s quite important to keep the window air conditioning coils clean to allow an effective exchange of heat without dirt and debris impairing or blocking the passages. Use a damp cloth to remove visible debris and get to the less-reachable parts with a soft toothbrush.

Give It a Rest

Do not leave your window air conditioner to run if you are not home for a longer period of time. As with everything else, these machines tend to wear out quicker with frequent usage. However, this shouldn’t always worry you as giving it proper maintenance is much more important.

Final Thoughts

Hopefully, we provided comprehensive answers on how does a window air conditioner works in order to make your living space actually livable during the hottest of summer days. Nonetheless, the most important thing to understand is that it uses two main air cycles for these purposes — the room and the hot air cycle.


Can you use a window air conditioner without a window?

As their name suggests, most window air conditioners are designed to run mounted in a window, and placing one such in the middle of your living room might leave you disappointed. This is mostly because their main function is to push the heat and humidity outdoors and there is no other way to redirect these if putting the unit in an enclosed area. You can use a portable air conditioner and run the hose out through a door.

How to vent a window air conditioner without a window?

In order to vent a window AC unit without a window properly, you need to know that the parts that usually sit outside will expel heat while running. As this heat is way stronger than the cooling air the unit generates, you might end up with a steaming hot room if not placed properly. This is why you need to invent some other creative way such as cutting a hole in the wall.

How much is a window air conditioner?

Depending on the quality and size of the area they are designed to call, window air conditioners cost somewhere around $150 to $600.