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

If you only need to cool one room in your house or office, a wall-mounted air conditioner is not a bad idea. It is a good alternative to portable and window air conditioners whose pros and cons I have written in this post.

Wall-mounted air conditioners should not be confused with through-the-wall air conditioners. They sound similar but are quite different.


While wall-mounted air conditioners have separate evaporator and condenser units, through-the-wall air conditioners have all the AC components in one unit. Through-the-wall ACs are installed on a specially framed hole in an exterior wall with a special sleeve to create an airtight seal.

Through-the-wall air conditioners are a good alternative to window air conditioners. If you don’t like the look of a window AC, you may consider a through-the-wall AC.

Wall-mounted air conditioners are a type of ductless air conditioners, also known as mini-split ACs. You only need to drill a small hole on the wall where the refrigerant line connects the indoor to the outdoor unit.

So, how do wall-mounted air conditioners work?

The fan pulls warm air from the room and passes it through the evaporator coil containing a cold refrigerant. The refrigerant absorbs heat from the air and cools it in the process. Cooled air is then circulated back to the house as the moisture in the air condenses and is drained out.

That is just a brief description of how the unit works. I will explain all the steps involved in more detail later on in this post.

Apart from wall-mounted ductless air conditioners, you can also consider floor-mounted, ceiling-suspended or even ceiling recessed air conditioners. Ceiling-recessed air conditioners are a good option for those who don’t like the look of suspended or wall-mounted AC units.

Again, floor-mounted ductless air conditioners should not be confused with portable air conditioners. Floor-mounted ACs are connected to the outside unit through a refrigerant line on the wall wall while portable ACs are self-contained.

Wall-mounted air conditioners have more BTUS and powerful fans than window and portable ACs and are therefore better at cooling. Their efficiency is also higher since they automatically turn off when the room is sufficiently cooled.

Wall-mounted air conditioners don’t need to be vented. The hot air is released through the condenser unit which is usually outside the house. Only portable air conditioners need to be vented.

In wall-mounted air conditioners, while the warm humid air is being cooled, the moisture in the air condenses into water droplets and is drained out through the condensate drain line. The condensate drain line can be indoors or outdoors.

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 “communication” 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.