How Your Air Conditioner Works

Originally published on November 12, 2012

Understanding AC Systems: A Behind-the-Scenes Look

While most people associate air conditioning with cold, the science behind making your home cooler actually deals with the transfer of heat. When that heat is lost, or removed, the remaining cold air cools your home.  In order to understand this system better, let’s look at the major components. Your central air conditioning system has two key components: the indoor unit, and the outdoor unit. They work in tandem to keep your home comfortable year-round.

Indoor Unit

The indoor unit is typically located in a closet or basement, and is near where your furnace filter is located. The unit consists of a coil box that contains what is called an evaporator.  The evaporator allows for the refrigerant – a cooling fluid inside the coil piping sometimes known by a brand name such as Freon™ – to evaporate and absorb heat. Once the heat is absorbed from inside your home, it leaves nothing but cool air to be sent back into your home.

Just as water absorbs heat from your stove in order to boil (or evaporate) refrigerant absorbs heat from your house. This means that both water and refrigerant turn from liquid to vapor as they absorb heat.

Outdoor Unit

The outdoor unit is usually located in the rear or side of your house and it is where the heat from inside your home is dispersed. It contains the compressor, condenser coil and a fan. The heat absorbed from your home’s air is transferred to the refrigerant and then pumped to the outdoor unit. As this heat is absorbed and moved by the refrigerant to the outdoor coil, it passes through the compressor.

The compressor in your air conditioning system has the primary job of moving the refrigerant throughout the system. This is important as we can then keep reusing the refrigerant to cool our house. The refrigerant is compressed to a higher pressure, and moved through the outdoor coil known as the condenser. As the refrigerant passes through the condenser, a fan delivers ambient air across the condenser coil causing it to cool.

As the process completes, the heat from inside your house is dispersed to the air outside your house. The refrigerant is then pumped back indoors and the whole process repeats.

Did you know that making your home cooler was actually less about increasing cold air and more about removing existing heat?

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33 thoughts on “How Your Air Conditioner Works

  1. I recently moved to my new home, I have been living in an apartment since then. I have a wifi enabled thermostat, I tried pressing “cool” in the option but the outside compressor is not working only the furnace seems to be running instead, do I have to turn on a switch to get my compressor going? Please help! Thanks.

  2. Is this normal?

    My AC cools fine but the blower insie the house seems to run all the time, even when the outside compressor turns off. The AC is set on AUTO, not RUN. If I turn up the thermostat the blower does shut off.

  3. Hello Rebecca Lockley.
    It may be due to the deep dirt on your filters. So it’s a possibility your A/C unit needs a deep clean cause of grime set on your Evaporator coil or condenser coil. On the other hand, it may be at the hand of a leak in your system or an obstacle obstructing the capillary tube because your filter drier or A/C oil is out of date. It may come up when your interior fan is burnt out or its power is cut off by terminals.

  4. The outside unit is working…but inside my house wont get cool…its 86 degrees inside…sounds like a pipe is freezing up behind the filter…what could be the promblem

  5. The unit outside keep working continously but the cool air inside the house is on and off until the temperature reaches the temperature set in the thermostat. Is this normal? Sometimes the cool air comes for about two minutes and stops for a minute and then comes again, but the unit outside never stops.

  6. The air isn’t coming out of the vents and it’s really hot in my house and I don’t know what to do I’ve turned it on and back off cleaned the top on the outside unit off and it’s blowing cold air out side and that’s usually hot air… my dad is terminally ill and he needs air (we have fans running but it’s not helping) anything else I can do to fix this problem…

  7. Hi I have darken A/c at my home 1.5 ton some time my outdoor unit not function hence we are unable to get cool air can some give solution for same please.

    What has to be done

  8. Every time the degree goes under the heat degree we set, the cold air comes out making the degree goes lower to 2 degree before the heat air comes out. Is it normal ? Thanks

    • It sounds like you have a heat pump type of unit. During times when the heat pump is not able to keep up with the required amount of heat, the thermostat setting has to be 2 degrees above what the room temperature is before it will add supplemental electric heat to make up the difference. We recommend working with a local contractor to select a different thermostat that can reduce the temperature swing you’re experiencing.

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