How a Wall-Mounted Air Conditioner Works, Pros & Cons


Wall-mounted air conditioners, also known as ductless mini-split systems, are popular choices for cooling individual rooms or zones. Here’s a summary of how they work, along with their pros and cons:

How a Wall-Mounted Air Conditioner Works

  • Indoor Unit: The system consists of an indoor unit, which is mounted on a wall inside the room you want to cool. This unit contains the evaporator coil, a fan, and control options.
  • Outdoor Unit: An outdoor unit, located outside the building, houses the compressor, condenser coil, and other key components.
  • Refrigerant Cycle: The wall-mounted AC system operates on the same basic refrigeration cycle as central air conditioners. Refrigerant is pumped between the indoor and outdoor units, absorbing heat from the indoor air and releasing it outside.
  • Air Distribution: The indoor unit blows cool air into the room while drawing warm air over the evaporator coil. This process cools and dehumidifies the indoor air.
  • Individual Zone Control: Ductless mini-splits allow for individual zone control. You can set different temperatures for various rooms or areas, enhancing energy efficiency and personalized comfort.


  • Efficiency: Wall-mounted ACs are highly energy-efficient, especially when compared to window units or portable air conditioners.
  • Zoning: They provide excellent zoning capabilities, allowing you to cool specific areas or rooms while leaving others untouched, saving energy.
  • Easy Installation: Installation is relatively straightforward, involving a small hole for refrigerant lines and electrical connections. It doesn’t require extensive ductwork.
  • Aesthetics: The indoor unit is sleek and unobtrusive, often mounted high on the wall. It doesn’t block windows or obstruct views like some other AC types.
  • Quiet Operation: Ductless mini-splits are known for their quiet operation, with the noisiest components, such as the compressor, located outside.


  • Upfront Cost: The initial cost of purchasing and installing a wall-mounted AC system can be higher than some other cooling options.
  • Installation: While easier than central HVAC systems, installation should be done by a professional, which can add to the cost.
  • Visible Indoor Unit: Although they’re less obtrusive than some other AC types, the indoor unit is still visible on the wall, which may not suit all interior design preferences.
  • Maintenance: Like all AC systems, wall-mounted units require regular maintenance to ensure optimal performance and longevity.

How a Wall-Mounted Air Conditioner Works


In a way, all air conditioners work the same way as I wrote here. Although there are minor differences, the principle of operation is the same.

A wall-mounted air conditioner just like all the other air conditioners is made up of 3 components:

  • Compressor
  • Condenser coil
  • Evaporator coil

The condenser coil and compressor forms what is known as the outside unit or a condenser unit. The inside unit (the one mounted on the wall) is the evaporator coil.

These components are connected together using copper tubes. The copper tubes (also known as refrigerant lines) are responsible for transporting the refrigerant from one component to another, forming a close-looped system.

A refrigerant is a chemical ideally with a low boiling point and high latent heat of vaporization. It changes state from liquid to gas and back to liquid again easily making it a good medium for heat exchange.

Freon (R-22) was the refrigerant of choice for many years but after it was established that it depleted the ozone layer it was phased out. Puron (R-410A) is now found in most modern air conditioners.

Let us now see how wall-mounted air conditioners work in order to cool your house one component at a time

1. The Evaporator Coil

The evaporator coil is the wall-mounted unit inside your house. It is a heat exchanger responsible for cooling your house.

Cold refrigerant (in its liquid state) enters the evaporator coil from the condenser coil while at the same time the fan is pulling warm air from the house. The warm air is passed through the coil where heat exchange takes place.

Heat in the indoor air is absorbed by the refrigerant and the cooled air is circulated back to the house. Since the air is humid as well, the moisture in the air condenses into water droplets that are then drained out through the condensate drain line.

Refrigerants have a low boiling point but high latent heat of vaporization (energy/heat needed to vaporize a liquid). This means that the refrigerant evaporates easily and in the process absorbs lots of heat from the indoor air.

After absorbing heat from the indoor air, the refrigerant evaporates and is ejected out of the evaporator in its gaseous state.

2. The Compressor

As I have mentioned, the compressor is found outside in the same housing with the condenser coil. After absorbing heat from the house (inside the evaporator coil), the refrigerant vaporizes and enters the compressor.

The function of the compressor is help the refrigerant dispose of that heat to the surrounding. You see, although the refrigerant is hot, the outside temperature would be hot as well since that would be during summer.

In thermodynamics, in order for heat transfer to be effected, there needs to be a temperature differential between the 2 mediums. Heat is transferred from a high concentration point to a point of low concentration.

The compressor compresses the refrigerant gas to increase its pressure. What you might not know is that increase in the pressure of a gas also results in an increase in temperature.

3. The Condenser Coil


The refrigerant gas therefore exits the compressor and enters the condenser coil as a high-pressure high-temperature gas. At that point, the temperature of the refrigerant is way more than that of the surrounding air.

Because of the temperature differential established, the refrigerant can now release its heat to the surrounding. A fan (known as a condenser fan) blows cooler air over the condenser coil which accelerates the rate of heat exchange.

The cooler air absorbs heat from the refrigerant and that is why if you stand next to the condenser unit you can feel hot air being blow towards you.

By the time the refrigerant is exiting the condenser coil, it will have turned back to its liquid state after losing most of the heat.

4. The Expansion Valve

Before the refrigerant enters the evaporator coil, it first goes through an expansion valve (commonly known as thermal expansion valve although there are other types of the valve).

An expansion valve is basically a small hole or restriction that controls the amount of refrigerant entering the evaporator. If too much refrigerant enters the evaporator, not all of it will vaporize meaning some of it will enter the compressor in its liquid state.

A compressor is only supposed to compress gases. Presence of a liquid in the compressor will damage it.

Apart from that, the expansion valve is used to further lower the temperature of the refrigerant. Even though at that time the refrigerant will have lost most of its heat, it still needs to lose more for proper cooling to take place.

When the refrigerant goes through the small opening, its pressure falls drastically. Since an increase in pressure also results in an increase in temperature, the opposite is also true.

The temperature of the refrigerant liquid falls dramatically as well and at that time the refrigerant is ready to go inside the evaporator coil for another round of cooling.

Types of Wall-Mounted Air Conditioners

There are 2 types/variations of wall-mounted air conditioners. You could 1 have inside unit connected to 1 outside unit or several inside units connected to 1 big condenser unit.

If you only need to cool one room, you only need to install one evaporator unit in the room you need to cool and one condenser unit. The condenser unit in this case will be a smaller and cheaper than one which would be needed to cool several rooms.

On the other hand, if you are considering wall-mounted (ductless mini-splits) air conditioners as an alternative to central air conditioners, you will need to purchase a big condenser unit and several evaporator units (one for each room).

One evaporator coil is not sufficient to cool the whole house. It will be overwhelmed by the cooling demands of the house meaning it will need to work harder effectively reducing its efficiency and lifespan.

Advantages of Wall-Mounted Air Conditioners

The following are the advantages of wall-mounted air conditioners compared to other air conditioners:

1. Saves Floor Space

Since wall-mounted air conditioners do not need any floor space, they are a good option for folks who do not like portable and central air conditioners which needs some sort of floor space in the house.

Just like packaged air conditioners, people who do not have a crawlspace for installing an evaporator coil will find wall-mounted air conditioners to be a great alternative.

2. Inbuilt Zoning

In central air conditioning, all rooms are cooled to the same temperature. While that is ideal for most people, there are those who would prefer having different temperatures for different rooms.

And that is where wall-mounted (and other mini-splits) come in. If you want your home office cooler than say the bedroom, you can do just that.

Each wall-mounted unit has its own remote control that you use to adjust the temperature requirement of each room.

3. Energy Efficient

Wall-mounted units are way more efficient that portable and window air conditioners. They will turn off automatically when the room is properly cooled and they also offer superior cooling.

Portable ACs are especially inefficient because they work by sucking air from the room before cooling it. That process creates negative air pressure inside the room and hence hot air will try to infiltrate the room from outside forcing the unit to work harder.

4. Low Maintenance

It is way easy to maintain wall-mounted air conditioners compared to central air conditioners. Central air has a network of ductwork which needs to be cleaned and fixed (in case of leaks), issues that are foreign to wall-mounted ACs.

In the case of window air conditioners, you may need to remove them during winter to prevent them from damage by extreme weather. Lack of proper sealing during installation may also allow cold air to infiltrate reducing the efficiency of your heating.

5. Easy to install

Wall-mounted air conditioners are way easier to install compared to central air or even through-the-wall air conditioners. You will only need to drill a small hole on the wall through which the refrigerant line will connect the evaporator coil to the condenser unit.

Through-the-wall ACs needs proper installation and insulation to ensure there is no ‚Äúcommunication” between the outside and inside air. Central air installation is labor-intensive meaning it is costly.

Disadvantages of Wall-Mounted Air Conditioners

The following are the disadvantages of wall-mounted air conditioners:

1. Not Visually Appealing

The main disadvantage of wall-mounted air conditioners that I can think off is how they affect the aesthetics of the house. For proper cooling, wall-mounted ACs are installed high up on the wall and are therefore quite conspicuous.

There are people I know who opted to go with central air for this very reason.  In areas like offices where aesthetics are not that important, these units work just fine.

2. High Initial Cost

If you are comparing between central air and window air conditioners (for each room), you will notice that the initial cost for the wall-mounted air conditioners will be higher.

The above statement is made in the assumption that the ductwork for the central air is already in place. If that is not the case then installation cost of central air will be way more than that of wall-mounted ACs.

3. Not Ideal for Large Spaces

Just Like window and portable air conditioners, wall-mounted air conditioners are not ideal for large spaces. They can only cool one room unlike central air which cools the whole house.

Note: When buying an AC be sure to check out its BTU rating. The high the BTU rating the higher its cooling potential.

If you need wall-mounted air conditioners to cool your whole house, you will need to install several of them (one in each room) and an even bigger condenser unit.

Wrap Up

And basically that is everything about wall-mounted air conditioners. I hope that this post answers what you were looking for.