How Does My Air Conditioning System Work? (Part 1)

A cool breeze on a hot summer day... Can you feel it? Isn’t it refreshing? The best part is that you’re inside your home cool and comfortable because you have an air conditioning system. But do you really know what it is doing? Or how it is doing it? Does it matter? Yes it does! Understanding how your cooling system works will help you in two ways: 1) You will understand why regular maintenance is a necessity, not just a luxury; and 2) You will know how to get the most out of every penny you spend in energy costs.

The Basics 

First let’s go over some basics. Every air conditioning system (also called a cooling system, or AC) must have a thermostat. The thermostat is how you tell your system when and how long to run by setting the temperature that you want in your house. Let’s say you want it to be 72 degrees inside. When the thermostat feels the air temperature rising above 72, it turns on the AC. The cooling unit then removes the heat from your house. Then as the thermostat feels the air cooling down to 72 degrees it turns off the AC. Simple thermostats allow the temperature to go up or down a few degrees from your set temperature so that your cooling unit isn’t turning on and off a lot. More advanced thermostats can calculate how often your AC needs to run in order to keep the temperature steady without that up and down temperature swing.

Air Conditioners – How do they work? 

For many people how an Air Conditioner works is a mystery, but isn’t that complicated. A cooling system has the following two parts: A Circulating Fan/Coil unit or ‘indoor unit’, and a Compressor/Condensing unit, or ‘outdoor unit’. (In most cases the Circulating Fan/Coil unit is inside your house. However if you have a ‘packaged unit’ then both parts are built together and are outside. For simplicity we will call them the ‘indoor unit’ and the ‘outdoor unit’.)

Here is a key to understanding how an Air Conditioner works: an AC does not make cool air, but rather it transfers the heat from inside your home to outside your home. Let me explain. 

The ‘outdoor unit’ is the heart of your cooling system. When the thermostat tells it to come on, then the compressor, which is like a pump, pushes refrigerant through a tiny nozzle as a mist into a coil in the ‘indoor unit’. This mist is very cold and it cools down the coil, which looks something like a car radiator. The fan in the unit pulls air from your house through a filter, and then through the coil. The hot air from your home warms up the coil as it goes through, but that cools down the air which is then blown into your house.

The refrigerant leaving the coil of the ‘indoor unit’ is now warmer and goes out to where the compressor is. Then it is pumped into another coil that surrounds the compressor. In this coil it is now a very hot liquid. Even on a hot summer day the air outside is still able to cool down this coil using the fan in the middle of the ‘outdoor unit’. Now the refrigerant has cooled down so the compressor pushes it back inside through the tiny nozzle in the ‘indoor unit’. And the cycle continues.

There’s just one more helpful detail to explain. When the ‘indoor unit’ pulls air from your home though the coil, it is not just removing the heat. It is also removing the moisture. Think of this: What happens on a hot day when you fill up a glass with ice water? It gets wet on the outside, right? That’s because moisture condenses on cold surfaces. Well the same thing is happening inside your indoor unit. Moisture from the air in your home is condensing on the coil. So if you come home on a hot, muggy day and the AC has been off, it might take a while after you turn it on for you to see the temperature drop on the thermostat. First your AC is removing the moisture from the air, and then it also gradually pulls the out heat out.

See? That wasn’t so hard! Now, what about the most important question: How does this help me? Are you ready to see how this will help you care for your system? Do you want to know how to get the most benefit out of what you pay for energy? We’re going to answer those questions in an upcoming post. So stay tuned! (UPDATE: You can now read Part 2 here!)

Do you have a question about any of this? Visit our Ask an Expert page and ask away!

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