How Does an Air Conditioner Work?

Air conditioners are so convenient that they may seem like magic, but the science behind how they work contains some fairly basic principles. At their core, air conditioner systems are made up of five general components:

• Refrigerant — Transfers heat from one place to another
• Compressor — Forces gas refrigerant into condenser unit at high temperature
• Condenser — Changes gas refrigerant into liquid while extracting heat
• Evaporator — Lets the refrigerant change back into a gas, which extracts heat from the environment for a cooling effect
• Expansion valve — controls the pressure of the refrigerant so that it evaporates indoors absorbing heat and condenses outdoors, extracting heat

A thermostat that turns on and off the AC unit according to the temperature reached inside can be considered a common sixth component. Each element above works with the others to make your home nice and cool when it is hot outside. The process may seem complicated, but it involves some pretty basic physical chemistry.

Three Take-Home Concepts

To even begin making heads or tails of how the components above make your home feel cool, you must understand three general concepts:

Temperature is relative and felt by heat exchange.

Temperature is a measure of how much energy an object has. When we touch something with more energy than us, we absorb the energy, and it feels hot to us. When touching something with less energy than us, it feels cold because it is taking our energy away. This fact is why when you jump into a hot bath with cold feet, the water can feel painful on your feet but not the rest of your body — your body is absorbing energy in different relative amounts.

Pressure changes can make liquids boil at different temperatures.

We may be familiar with water boiling at 212 °F, but we may also have heard that water boils at a lower temperature at higher altitudes. This effect occurs because the air pressure is “pushing” less on the water, letting it become a gas at a lower temperature.

Someone can use this effect to change a substance like refrigerant from a liquid to a gas by changing the pressure while keeping roughly the same temperature.

Changing states from a liquid to a gas or a gas to a liquid can create different temperatures.

This concept is the least intuitive of the three to understand. Put simply, a liquid becoming a gas takes a lot of energy. Letting the bouncy molecules of a gas settle into a liquid can add energy. As we know, energy differences translate to temperature differences.

The easiest example would be to think of a compressed spray can. When you press the nozzle, you reduce the pressure in the can, and the liquid becomes a gas. The act of letting the liquid evaporate sucks up energy from the bottle, which sucks energy from your hand and feels cold.

Putting these three concepts together, AC systems change refrigerants from liquids to gases at crucial spots using pressure changes. Heat energy is pulled out of your house and into the condenser where most of the heat is blown off into the environment. If that is a lot to take in, here is what each component does in more detail:

Compressor

Compressors can be thought of as the engine that drives the AC process. The compressor pushes the refrigerant along in a closed pipe throughout the entire system. Refrigerant is put under high pressure in the compressor, forcing it into the condenser coils.

Condenser

When the refrigerant comes out of the compressor at high pressure, it gets slowed down inside the long condenser coils. As stated before, the increase in pressure changes the gas refrigerant into a liquid, which creates heat. This heat is pulled out of the condenser coils by touching metal fins, and an exhaust fan blows across the fins to push the heat into the outside air.

Expansion Valve

Once the liquid refrigerant leaves the compressor, it reaches the expansion valve at high pressure. On the other side of the expansion valve, there is less pressure since the refrigerant is coming through slowly.

An example of this effect can be seen when you spray water out of a hose. The water comes out at high pressure in a single stream, but then it turns into droplets and even some water vapor once it is allowed to reach the air. Similarly, as refrigerant crosses through the expansion valve, it starts to turn back into a gas.

Evaporator

Once the refrigerant reaches the other side of the expansion valve, it has more room to move and can start becoming a gas again. It soon reaches the evaporator unit, which lets the refrigerant expand even more and turn completely into a gas. This takes heat out of the surrounding areas. As mentioned before, this makes the evaporator coils feel cool if someone were to touch them. A blower forces air across the evaporator, which becomes cooled and circulates throughout the home.

Back to the Compressor

The gas that crosses through the evaporator still feels moderately cold and is at a low pressure. Since the compressor is pushing the refrigerant out downstream of the line, it also pulls the refrigerant upstream into the compressor and the cycle starts again.

In essence, the only real difference happening is that the pressure on the refrigerant is changing at different spots, which allows it to gain and lose heat. These heat differences drive the AC effect and lowers the overall the energy inside the home to a more comfortable level.

Just reading this guide probably hasn’t made you an expert in all things AC. If you need an air conditioner replacement, it’s best to leave it up to the pros.

Are you in the market for a new heating and air conditioning system? Click here to get free custom quotes from reputable HVAC contractors. You’ll receive upfront pricing without having to invite a contractor to your home or even enter your contact information!

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