How Does an Air Conditioner Work?

Air conditioners (AC) work hard to keep your home comfortable, even on the hottest summer days. Unless you are an HVAC technician, you likely don’t know exactly how an air conditioner works. Knowing about how the system works can help you use it more efficiently, and understand why maintenance is important. So we’re going to break it down from start to finish.


Starting Up

Starting the air conditioner is the most strenuous part of the cooling cycle. Think about starting your AC as you would starting your car. The battery can run a long time on a continuous charge, but the initial start of the car takes a significantly larger chunk of juice to get it going. Air conditioners work in a similar way. The first thing you should know is that there are 4 core parts of the AC:

  • Compressor

  • Condenser

  • Evaporator

  • Fans

All of them are interconnected with each other and if one goes out, the whole system stops working. We’ll cover what each of these parts do as we go through the process.

The Cooling Process

Air conditioners are commonly seen as systems that create cool air and blow it into the home. Actually, air conditioners pull heat out of the air and blow it out of the home. The remaining air to be circulated is now cooler, thus lowering the temperature of the home. This is why the return ducts are so vital to the functioning of the system. A closed duct means a less efficient system. This is also why smells from anywhere in the home will eventually reach the rest of the home if there for a long enough time.

  1. Hot air is pulled into the system – Using fans, the warm air in your home is pulled into the system to be cooled and recirculated.

Refrigerant Gauges

  1. Refrigerant/Freon cools the air – The refrigerant, also known as Freon, flows through the evaporator coil. This refrigerant’s only job is to absorb the heat from the air through a natural process called phase conversion. During this stage, the liquid is converted into a gas through a natural process called evaporation. It is now a cool, low pressure gas ready to be circulated.

Central AC Unit Compressor

  1. Cool, low pressure gas is converted back to liquid – At this stage, the gas is not quite ready to be distributed throughout your home. Although it could be released through fans, this would not be an efficient way to cool your home. So, the gas is now moved into the next area of the air conditioner through ducts throughout the system. The ducts carry the cool, low pressure gas to the compressor. The compressor’s job is to move the gas into a chamber and compress it down to the point that the gas is a liquid. The compression process produces some excess heat, but this heat is then taken out later and is blown outside.

  2. Removing the extra heat – All of this heat is then taken out by the condenser coils, which absorb heat. The heat is then blown outside using a fan.

  3. Cooling of the gas changes it to liquid – All of the heat that was expelled from the system means that the gas is now cooling. When gas cools, it turns into a liquid. Similarly, when it rains outside the temperatures generally drop.

  4. Rinse and repeat – Now we have this cool liquid again. The liquid is then converted to a gas again through phase conversion.

AC Fan

  1. Cool air – At this point, the cool air is then taken through the ductwork via fans. The air comes out of various vents in your home, wherever you have them installed.

A similar process occurs with window AC units, but in a much smaller box than a full-sized central air conditioning system. In fact, you can pop the cover off of the front of many window units and even see the evaporator coil. We recommend you not touch it, but if you use a laser thermometer you can see the temperature is that of a refrigerator. This is because refrigerators work in a very similar way, except they only cool inside of the refrigerator.

Where Does the Filter and Maintenance Come in?

Your filter is vital to the efficiency of your system. Imagine the air coming into the system was not filtered and carried dog hair, dust, and other debris with it. When the air comes over the evaporator coils, it is very difficult to cool the air. While most of the air may still cool off, this air is taken into the compressor where it’s converted to a dirty liquid. The whole process begins and ends with dirt, reducing the effective life expectancy of your system.

The filter’s core job is to filter in the air intake. The filter has tiny holes in it that only allow air to pass through. Everything else is caught on the material, which depends on which type of filter you use. Oftentimes they are made of cotton. Eventually, this filter gets clogged up with too much dirt and debris. When this happens, air can no longer flow efficiently into the system, meaning more hot air in your home.

We always recommend that you have system maintenance performed regularly to keep your air conditioner running at peak efficiency. Over time, it’s possible that some dirt can make it into the system. This dirt needs to be cleaned out and removed. Similarly, when the system is off, air can casually breeze into the system through some fans. Maintenance is also when we ensure that your refrigerant levels are good, and that all of the parts are functioning properly.


To summarize, the hot air brought into the system is cooled via the refrigerant in the evaporator coil. From here, it moves into the compressor, where it is converted into a liquid. The excess heat is removed by a condenser coil and a fan. The liquid is then reverted back to the gas through phase conversion for distribution through your home. Without cleaning or replacing your filter and performing regularly scheduled maintenance visits, your AC system will not run at peak efficiency, costing you money and a loss of comfort.

Contact Comfort Pro today if you have any questions about your system or would like us to look at your system for repairs or maintenance.

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