How do Portable Air Conditioners Work? [Simple Guide]

Written by: Paul Cathro

Updated on: December 23, 2022

Learn how portable air conditioners work their magic in our latest guide. We also answer the most common questions about these often misunderstood devices.


A portable air conditioner is a great way of cooling one room or a single space in your home.

They're simple to use and incredibly convenient.

Much more effective than a regular fan and much easier to install than other types of air conditioners, they can be real lifesavers in certain situations.

But, to remain portable they need to do their job in a unique way and certain concessions need to be made.

In our guide, we explain exactly how portable air conditioners work. From lowering the temperature of a room to removing humidity from the air, we have a simple explanation down below.

The Key Components of an Air Conditioner

Explaining the roles of the key components of a portable air conditioner is a great way to understand how they work.

By following the path of the refrigerant through the air conditioner and understanding its different stages of life, you should get a good idea of what's happening inside.


Refrigerant is a chemical compound that absorbs heat. R-22 (Freon) and R410A (Puron) are the two main types.

New AC units use Puron as it is better for the environment and provides more efficient cooling.

The refrigerant's role is to travel through the unit (starting in the evaporator coils) while changing its state from a low-pressure gas to a high-pressure liquid.

While doing this it performs to key jobs. It first absorbs heat (in the evaporator coils) and then finally releases heat.

It releases heat in the end by means of condensation. This then makes it cool down again and the process repeats.

The refrigerant cycle is constant and continuous. Cooling the hot air by absorbing heat and then releasing the heat and cooling down again to preform the process again.

Evaporator Coils

This is the first port of call for the warm air once it enters the AC unit.

The evaporator coils are incredibly cold because they contain refrigerant. They are usually made of aluminum or copper.

The refrigerant contained in the coils absorbs the heat from the air, cooling it.

The cool air is then blown back into the room while the by-product condensation (water) is collected and drained.

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This is the noisy part of the AC system that in traditional units is placed on the outside of a building.

Up until this point in the AC refrigerant cycle, the heat has been absorbed in the evaporator coil (by the refrigerant).

Next, the refrigerant is heated even more. It's already hot after absorbing heat from the warm air, but it needs to be much hotter than the temperature outside.

The compressor does this job by increasing the pressure on the refrigerant.

The compressor puts so much pressure on the refrigerant that it changes state from a liquid to a gas.

In the process, of changing from a liquid to a gas under extreme pressure, the temperature of the refrigerant increases significantly.

Condenser Coil

The next stop for the now pressurized, hot and gaseous refrigerant is the condenser coil.

The condenser coil's role is to dispose of this heat. It does this by cooling the refrigerant down.

The heat is condensed and takes the form of water (condensation) which needs to be disposed of by the portable air conditioner via draining.

After being cooled, the refrigerant turns back into a liquid. Now, it can start the process all over again.

The Expansion Valve

The often overlooked but crucial component is the expansion valve.

The refrigerant has just been cooled significantly by the condenser coil but it's still a bit too warm to go back into the evaporator coil and cool the hot air again.

The expansion valve cools the refrigerant down to its original temperature by decreasing the pressure on it (essentially allowing it to expand).

The refrigerant is again now icy cold and a liquid. It heads back to the evaporator coil to start the process all over again.

The Basic Operation of a Portable Air Conditioner

Portable AC units generally perform 3 tasks:

  • They lower the ambient room temperature (heat-pump models can raise the temperature too)
  • They remove moisture from the air (dehumidify)
  • They circulate air (via a fan)

To lower the air temperature a portable air conditioner works using the same principles as any other type of AC.

It just doesn't do it quite as efficiently because it needs to remain portable.

So, how does a portable AC work?

How Does a Portable Air Conditioner Cool Air?

  1. 1
    In order to cool the air and lower the ambient temperature, an air conditioner first needs to "collect" the warm air. It pulls the warm (and usually humid) air inside using a fan.
  2. 2
    Once warm air enters the portable air conditioner it then needs to be cooled. The evaporator coils are filled with very cold liquid refrigerant that performs this task. The heat from the air is absorbed by the refrigerant.
  3. 3
    The now cold air that has been cooled by the refrigerant is blown back into the room via a fan. Condensation is collected as a by-product of the hot air cooling and is drained via a hose or drip tray (usually). 
  4. 4
    The now hot refrigerant (it has absorbed the heat from the air) needs to be cooled so that it can perform the cycle again.
  5. 5
    The refrigerant enters the compressor where the high pressure increases the temperature even more. It needs to get very hot before it can become very cold.
  6. 6
    The now very hot, gaseous, and pressurized refrigerant then comes into contact with the very cold condenser coil which turns the refrigerant back into cold liquid. Like the evaporator coil, the condenser coil is made of copper or aluminum and contains very cold refrigerant.
  7. 7
    The refrigerant isn't quite cold enough too enter the evaporator coil again so it is cooled further by the expansion valve. The expansion valve decreases the pressure on the refrigerant, allowing it to cool to its extremely cold original state. It then enters the evaporator coil again to start its journey once more.

How Does a Portable Air Conditioner Dehumidify?

Portable ACs are generally really good at dehumidifying air. 

Larger models can remove around 4 pints of water from the air every hour! Now that's some serious moisture removal that has an effect in even the most humid of climates.

Dehumidifying warm air is actually a nice bonus side-effect of cooling air so they do this naturally. However, you can set them to work in 'Dehumidify Only' mode which uses slightly less energy (it's still very energy hungry though).

They gather this unwanted moisture (that's been stripped from the humid air) in a variety of ways.

The leading portable air conditioners can actually make the unwanted water evaporate. This gas then needs to be vented somewhere outside.

Other methods of water disposal involve simply collecting the waste water in a tray (which you must then empty) and using a built-in pump to force the water out of a hose.

What Does A Portable Air Conditioner Need to Work?

While all models are different and therefore have different requirements, most are quite easy to set up.

The key point of any AC unit is to take away the hot air during the cooling process. That means that the unit must find a way of moving the warm air to a different location.

Usually, this requires venting through a window to the exterior of the property, although some models have an exhaust through a wall or drop ceiling.

Don't miss our guide to venting portable AC for more details.

portable ac and cooling fans

Once the exhaust has been set up, you simply plug the portable AC unit into a power outlet, switch it on and then it will begin cooling the space straight away.

The majority of portable AC units are able to be used on a standard 115V or 120V power circuit. That means that no special wiring or outlets are required.

If the unit uses more than 14,000 BTUs though, it may need to be run on its own unique circuit, so it’s important to look at the owner manual to ensure that your choice of model is suitable for use on your own specific outlet type.

As all air conditioners use a lot of energy when they are operational, you’ll need to keep any other devices with a high energy requirement on a different circuit. This will prevent the overloading of a single circuit in your home.

Using Portable AC Units In Several Rooms

Another commonly asked question is how well do portable AC units work when it comes to cooling multiple spaces in the home at once.

Again, all units are different but depending on which one you choose, it may be capable of cooling multiple rooms.

Similar to standard window air conditioners, a portable unit is capable of cooling its immediate surrounding area.

However, the cool air will be unable to travel down a long hall or a doorway which isn’t connected directly to the space in which it is located.

You may be able to cool two spaces that have a large opening between them, however, that cooling may be uneven.

The good news is that if you are only cooling a small space, a large unit won’t be necessary. A small and compact model should do the job perfectly well, and you might even be able to use a completely different kind of air conditioning unit.

Recommended: Check out our recommended quiet portable air conditioning units on the market right now.

What's the Difference Between Dual Hose & Single Hose Portable AC?

A portable air conditioning unit cools down your room by using a hose which is vented through to the exterior of the property.

A portable unit will have either a single exhaust hose to allow hot air to escape or two hoses.

Single Hose Portable AC

These models are cheaper and more common than dual-hose models.

The single-hose vents the hot air and allows it to escape usually through a window exhaust (but sometimes in the wall or door).

This simple method essentially takes hot air and pumps it outside without replacing the air. This has a drawback.

The drawback is low pressure.

This isn't noticeable to you or me in terms of ear pressure or anything like that but the in-balance in pressure needs to be addressed.

What tends to happen is that warm higher pressure air is sucked into the room from other rooms or any air gaps that exist.

This problem can be remedied by ensuring there aren't any significant air gaps in the room in which the portable AC is working.

Portable AC vented through a wall

Dual Hose Portable AC

These models are more expensive and slightly harder to install as you have two exhausts to cater for.

However, they are more energy efficient and can usually cool rooms faster than single hose units.

If a unit comes with two hoses, one of them will bring in air from outside the home while the other exhausts it back to the exterior.

Dual hoses don’t create a negative pressure, unlike a single hose model. This means they can achieve higher EER ratings for energy efficiency.

It isn’t a good idea to try to lengthen your air conditioner’s hose. It has been designed to be a specific length in order to allow the appliance to operate efficiently.

If you extend the hose, your unit may overheat and the manufacturer’s warranty may be voided.

How Often do You Have to Drain a Portable Air Conditioner?

A key task that any portable air conditioning unit must do is remove moisture from the air.

That moisture needs to go somewhere and that will depend on the type of appliance you have.

Self-evaporative models are advanced designs that automatically evaporate moisture from the exhaust hose together with the warm air.

With this type of unit, you’ll rarely need to empty the water tank and the amount of ongoing maintenance is minimal.

Models that have a condensate pump and gravity drain use a drain hose attached to the appliance to remove water. The hose allows the moisture to drain out into a floor drain or bucket.

There are also some models that require the water to be removed manually. Sometimes, this could be as frequently as every eight hours.


Frequently Asked Questions

Here, we’ll answer some of the most commonly asked questions that you may have about portable AC units and how they work.

1. How Can a Portable AC Unit Be Moved to Different Rooms?

Unlike window units which are very heavy to lift and move, a portable AC unit will usually be fitted with a handle or wheels or both.

This allows for easy movement into different spaces and rooms without needing to lift any heavy appliances.

2. What Size of Unit do I Require?

The cooling power of a portable AC is measure in BTUs (British Thermal Units).

A higher number of BTUs means more powerful cooling and the more space it’s capable of cooling.

These figures below are a basic guide to possible requirements for the size of your space:

7,500 BTUs – 150 square feet
9,000 BTUs – 200 square feet
10,000 BTUs – 300 square feet
12,000 BTUs – 400 square feet
13,000 BTUs – 450 square feet
14,000 BTUs – 500 square feet

Remember, that fewer BTUs will be needed if you’re living in a cooler area or if you’ll only be using your unit during the evening.

If you’re living somewhere very hot or are going to use the unit during the middle of the day, a higher number of BTUs may be needed.

It's also really important to match the cooling power of an air conditioner to the room size as closely as possible.

Get one that's too small and it just won't work effectively. Get one that's too big and it just won't work efficiently.

3. Can I Use My Portable Unit With a Crank Window?

If you have a crank or casement window, you won’t be able to find any portable AC units that come with a suitable window kit to fit your window type.

While some customers make their own solution by using Plexiglas and covering their whole window before cutting a hole into it for the exhaust hose, this may not be something you want to do.

Instead, you may wish to consider investing in a floor or free-standing air conditioning unit to cool your space effectively without needing to fit it in your window.

4. Will I Need to Take the Screen Off My Window When I Use a Window Kit?

If you have a screen on your window but want to use a window kit to connect your air conditioner to the window, you’ll probably need to know if it has to be removed to use the window kit.

The good news is that most people are able to leave their screen in place in their window since the portable AC unit’s exhaust hose rarely extends out of the window.

You should, however, check-in your unit’s product description before you buy to ensure that yours will not need the screen to be removed.

About the Author Paul Cathro

Paul is an ex-HVAC engineer with 5 years 'in the trade'.

He acquired in 2022 and aims to make it the internet's most comprehensive HVAC resource for small homes in the next few years.

You can learn more about Paul's story here.

Browse his published work on the website here.

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