How Ductless Air Conditioners Work – Pros & Cons

Do Ductless Air Conditioners Work Well?


Ductless air conditioners, also known as ductless mini-split systems, offer efficient cooling without the need for traditional ductwork. Here’s a summary of how ductless air conditioners work:

1. Indoor and Outdoor Units:

  • Ductless air conditioners consist of two main components: an indoor air-handling unit and an outdoor condenser unit.
  • The outdoor unit contains the compressor, condenser coil, and a fan, while the indoor unit houses the evaporator coil and a blower fan.

2. Refrigeration Cycle:

  • The cooling process in a ductless system operates on the same basic refrigeration cycle as traditional air conditioners.

3. Heat Absorption:

  • Warm indoor air is drawn into the indoor unit by the blower fan.
  • The indoor unit’s evaporator coil contains refrigerant, which absorbs heat from the indoor air as it passes over the coil.

4. Refrigerant Flow:

  • The heat-absorbed refrigerant becomes a low-pressure, cold gas and flows through a line set (copper tubing) to the outdoor unit.

5. Compression and Release:

  • In the outdoor unit, the compressor pressurizes the low-pressure refrigerant gas.
  • This process raises the temperature and pressure of the refrigerant, turning it into a hot, high-pressure gas.

6. Heat Dissipation:

  • The hot refrigerant gas is then pumped through the outdoor condenser coil.
  • The fan in the outdoor unit blows outdoor air over the condenser coil, releasing the absorbed heat into the outside environment.

7. Return to the Indoor Unit:

  • After releasing heat, the refrigerant returns to the indoor unit as a high-pressure, warm liquid.

8. Expansion Valve:

  • The expansion valve, located in the indoor unit, rapidly reduces the refrigerant’s pressure and temperature before it enters the evaporator coil again.

9. Cooling the Air:

  • As warm indoor air is drawn over the evaporator coil once more, the refrigerant absorbs heat from the air, cooling it.

10. Blower Fan: – The blower fan in the indoor unit then circulates the cooled air back into the living space, creating a comfortable indoor environment.

11. Temperature Control: – Ductless systems are equipped with a thermostat or remote control that allows users to set and maintain the desired indoor temperature.

How a Ductless Air Conditioner Works

Just like a central air conditioning system, a ductless air conditioner is made up of the following components:

  • Refrigerant
  • Compressor
  • Condenser coil
  • Expansion valve
  • Evaporator coil

A refrigerant is the gas which moves throughout the other components (connected using copper tubes in a closed-loop system) as it changes from liquid to gas and back to liquid again.

Refrigerants have a low boiling point which allows them to evaporate easily. As the refrigerant evaporates, it takes away heat from the surrounding air thereby cooling it in the process.

Freon has been the refrigerant of choice for many years but because of its effects on the ozone layer it is no longer being produced. More information on that in this post.

Let us now look at how ductless air conditioners cool your house starting from the compressor.


The compressor works like a pump, only that it pumps the refrigerant throughout the closed-loop. It is part of the outdoor unit together with the condenser coil.

The compressor receives a low-pressure high-temperature refrigerant from the house where it is compressed to increase its pressure. Why do we need to compress the refrigerant though?

When a gas is compressed, its pressure increases. As its pressure increases, its temperature increases as well.

It is important to increase the temperature of the refrigerant so that it can lose heat from the house to the surrounding. The outdoor air is hot but we need the refrigerant to be hotter than that.

The reason for that is because in thermodynamics, heat is transferred from a point of high concentration to a point of low concentration.

2. Condenser Coil

High-pressure superheated refrigerant gas enters the condenser coil from the compressor. As you can tell, the function of the condenser coil is to turn the refrigerant from gas to liquid. For that to happen, the refrigerant needs to lose heat to the surrounding air.

A fan installed on the condenser unit blows cool air over the condenser coil. The air being blown by the fan carries with it heat from the refrigerant and dissipates it outside. That is the reason why the air around the condenser unit is usually hot.

The condenser coil comprises of many loops of a copper tube which increases the surface area of the refrigerant being in contact with the air being blown by the fan.

By the time the refrigerant is exiting the condenser coil, it will be almost in its liquid state, having lost a lot of the heat it had.

3. Expansion valve

An expansion valve is a small restriction installed just before the evaporator coil. It controls the amount of refrigerant getting to the evaporator coil.

If the refrigerant is not enough, the room will be undercooled. If too much refrigerant is let through, not all of it will manage to evaporate.

Failure of the refrigerant to fully evaporate means some liquid will go back to the compressor. Presence of liquid in the compressor will damage it.

The expansion valve also lowers the pressure of the refrigerant. When the pressure is reduced, the temperature of the refrigerant also falls drastically.

A low-temperature refrigerant increases the efficiency of the heat exchange between the hot indoor air and the refrigerant.

4. Evaporator Coil

An evaporator coil works the same way as a condenser coil but now in reverse. Since the refrigerant is now in its liquid state, the idea is to have it absorbs heat from the surrounding air and as it evaporates, the surrounding air is cooled.

Evaporator coils are equipped with a cylindrical fan known as an impeller fan. The room will also have a thermostat which senses the temperature of the room and turns the air conditioning system on and off.

As I had mentioned earlier, a ductless air conditioner can either have one or several evaporator units connected to the outdoor condenser unit. If you have an evaporator unit for each room, it means you will also have a thermostat for each room.

Once the thermostat senses that the air in the room is getting hot (relative to its setting), it will signal all the air conditioning systems to start running.

This means that if you have several evaporators in a ductless AC system, some evaporators could be running while others are off.

The evaporator fan pulls warm air from the room and forces it through the now cold evaporator coil. Heat from the indoor air is absorbed by the refrigerant which then evaporates and is sent back to the compressor unit.

The fan then blows the now cooled air back to the room and the process continues until the room is fully cooled.

Types of Ductless Air Conditioners

The following are the different types of ductless air conditioners:

1. Wall-Mounted Ductless AC

These are the most common installation of ductless air conditioners. The evaporator coil is installed on the wall of the room it is supposed to cool.

2. Floor-Mounted Ductless AC

These are mounted on the floor of the room they are supposed to cool/heat. They are especially great for seniors who would like to remove and clean the air filter regularly.

3. Ceiling-suspended

As their name suggests, these air conditioners are suspended from the ceiling of the rooms there are installed. Cooled air or heat is therefore very well distributed throughout the room.

4. Ceiling-Recessed

If you don’t like the appearance of the wall-mounted, floor-mounted or ceiling-suspended unit, this is the installation to go with. It hides most of the evaporator’s body inside the ceiling

Pros and Cons of Ductless Air Conditioners

Are ductless air conditioners worth it? Should you go with ductless air conditioning systems or opt for the more traditional central air conditioning systems?

Let me tell you about their advantages and disadvantages and maybe that will help you to decide.


The following are the advantages of ductless air conditioners:

1. Integrated Zoning

One of the main advantages of ductless air conditioners is that they allow you to zone the different rooms in your house at different temperatures. Each room has its thermostat and remote control for adjusting the temperature unlike in central air where the entire house is set at the same temperature.

If you therefore want your home office to be cooler than other areas of your home, you will only need to set the thermostat as such.

2. Energy-efficiency

You would be surprised to learn that 20-30% of the cold air or heat in central air conditioning units is lost to leaks in the air ducts. That loss will also be reflected in your energy bill.

Ductless air conditioners are therefore more efficient since there is no heat/air lose. You can also turn off cooling in rooms that are not currently occupied.

3. Easy installation

If you ask someone who has installed a central air conditioning system, they will tell you that the process takes long (by a professional) and is also very invasive. The ducts need to go through walls, which takes a lot of time and money.

With a ductless air conditioning system, you will only need to make a small hole on the wall to connect the indoor unit to the outdoor unit and you are set to go.

4. They can cool and heat

Most ductless mini-split air conditioning systems also work as heat pumps. This means they can not only cool your house but they can also heat it.

During the cold weather, ductless AC systems will heat your house while during hot summer months they will remove heat from your house.


So, what can make you opt not to install ductless air conditioning systems? The following are the disadvantages of ductless air conditioners

1. They are Quite Conspicuous

One thing to note about ductless air conditioners is their imposing presence in the room they are installed to cool. Wall-mounted and floor-mounted ductless ACs are especially conspicuous which is less than ideal for most people.

Worse enough, there are no ways to conceal these indoor units; you need them uninhibited by objects for free circulation of air to occur.

With central air conditioners, the indoor unit is concealed somewhere in the attic or closet. It therefore does not mess with you house décor.

2. Can be Costly

If you have an old house with existing ductwork, a central air conditioner would be the most cost-effective air conditioner to install. Removing the old ductwork and installing a new ductless air conditioner will be costly.

However, when comparing the cost of installing air conditioning in a new house, a ductless air condition system is cheaper compared to a central ac system.

3. Regular Maintenance

Ductless air conditioners need regular maintenance to clean the air filters, otherwise they will not work properly. The good thing is that that is actually something you can do on your own and you don’t need to call a technician

4. May Need Fuel Backup

If you live in a very cold area and opt to install a ductless air conditioner, you will most likely need a fuel backup to run ductless heat. I would however advice that you consult an HVAC specialist if you live in such a place.

Wrap Up

And basically that is everything in as far as ductless (mini-split) air conditioners are concerned. I hope you found this guide helpful