How AC Works 2018-05-18T06:12:11+00:00


Air conditioning systems use a chemical  known as a REFRIGERANT to remove heat from the air. (You might have heard of Freon. People think Freon is being phased out, but truth be told Freon is basically the brand name of a refrigerant made by DuPont)

The other type, water-cooled air conditioning systems, are central systems found primarily in large buildings. The difference with these systems is that instead of using refrigerant to remove heat, the system uses water.

On this page, we’ll focus on the more common air-cooled design and how Air Conditioning works with those systems.

In  your air-cooled AC system, refrigerant is the central component that produces a cooling effect. Refrigerants are chemicals that have an interesting and useful property: they can be converted from a gas to a liquid (and back again) relatively easily. As the refrigerant changes form (as well as temperature and pressure) it is capable of both absorbing heat and releasing it. Refrigerant is added when your system is installed, and cycles continuously (in various forms) through the components of your AC unit in a closed loop throughout the life of your system. Hopefully you never lose any of this gas.

Your air conditioner is designed to move heat from the air inside your space, and then release it outside the building. That’s why your air conditioner  has both indoor and outdoor components. The compressor and condenser are outside, and the evaporator/air handler is located inside. Most people know about the outside unit, but many people don’t know about the “business end” where the actual cooling takes place.

How AC Works: The Process and Most Important Components

The process of cooling the air in your space is a continuous cycle. Its like an automotive racetrack, the refrigerant just keeps going in a continuous loop.

So how exactly does this looping system cool my house?

Let’s start with the EVAPORATOR COIL, which does the actual cooling in the indoor unit. It looks like a car radiator.  But because it’s “in” your duct work,  you can’t see it. Even the winter furnace’s heat goes though this, while the AC sits idle.  The refrigerant is a high-pressure liquid when it reaches the evaporator coil. As it travels into the coil, it goes through a metering device, changing the refrigerant from a liquid to a gas and chemically causing cooling as it becomes a gas and removes heat from the surrounding air in the process. The structure of the coil with all those fins provides a lot of surface area for air to move over the coils so that heat can be absorbed. This is where the cooling happens, and as a side benefit, dehumidification also takes place.

When the Freon leaves the evaporator coil, the refrigerant is now a cool, low-pressure gas, which makes its way to the compressor. This pipe is usually identified by the black foam insulation, heading towards your outdoor unit (condenser).

The COMPRESSOR (found in the condenser) is thought of as the “heart” of the air conditioner. It’s the compressor’s job to “pump” the refrigerant through the system.

The compressor literally “compresses” the low-pressure gas refrigerant into a hot, high-pressure liquid, which then flows into the condenser. Your AC has another “coil” in the outdoor unit called the CONDENSER COIL. This structure (along with the help of fans) releases the absorbed heat, where it dissipates into the air outside. Your outdoor unit’s fan moves air through the condenser coil. This coil’s delicate fins are usually visible on the side of the outdoor unit. Some units have a louvered protective cover and you won’t be able to see the fins. If you can see these, you can clean them, but be careful not to damage the coil by bending fins over. DO NOT USE A HIGH PRESSURE WASHER!  Thumb pressure on the end of a hose is all you need.

How Cool Dehumidified Air Moves Throughout Your Home

Those evaporator and condenser coils have important work to do absorbing and releasing heat… but they need some help to get it done. That’s another important part of how AC works: both your indoor and outdoor units have fans the help with the process. The outdoor fan blows air over the condenser coils to help release heat. The indoor fans which are part of the indoor air handling unit (usually your furnace blower) move air over the evaporator coil and blow cooled air into your ducts and ultimately into the rooms of your home.

Air flow is one of the most critically important aspects of how your air conditioning works. Make sure you have a new clean filter, which will also help to remove moisture.

Here’s another way of thinking about it.

An air conditioner is a whole house dehumidifier with the added benefit of dropping the temperature in your house. Because the evaporator’s working temperature is in the upper 30 degrees, it’s probably below the dew point temperature. Therefore, warmer humid air condenses,  removing moisture from the air which accumulates on the cold evaporator coil. Moisture then flows down the evaporator onto a collection pan and is drained away.

Here’s The Take Away…

What we’ve provided here is a very basic explanation of your home’s cooling.

Now that you have a basic understanding of how AC works, you can avoid being taken for a ride if a problem should arise with your system.

Here’s one example and it’s a common one. You notice that your AC has not been cooling as well as it used to. It’s not a sudden breakdown; it seems to be happening gradually. You call someone to take a look and they give you what seems to be good news: the problem is only a low level of refrigerant. You can just add more; it’s a quick fix and not very expensive.

Wait a second! You just learned that refrigerant cycles through your system in a closed loop. So why is it low? That happens when your system develops a refrigerant leak. If you just add more without fixing the leak, the problem will only happen again. Certain vendors might neglect to mention that.

If this has happened to you, it’s time to think about switching vendors. That may seem like a hassle, but it isn’t if you know the right way to go about it.


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