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How Does Car Air Conditioning System Works


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Laws of physics

  • Heat travels from a hotter place to a cooler spot
  • Change of state - (a) when water is heated up it absorbs the heat energy & evaporates or boil (gain heat)
- (b) upon evaporation, the liquid becomes a gas/steam
- (c) if you place a cool piece of glass over the steam , it condenses into water droplets. (lose heat). The water changes state again, from gas to liquid

An AC system uses these principles to cool the car’s cabin. The objective of the ac is to move the hot air inside the car to the outside of the car. If we can move this hot air mass quickly enough & efficiently, we get nice cold air in the cabin.

Instead of using water, a car’s ac system uses a chemical called refrigerant ( R134a ). It has a funny characteristic, it can change state very quickly from liquid to gas state & vs versa. In liquid form the refrigerant is cold & when it absorbs heat, it can quickly evaporate or boil & become a gas. When in gas form & if it is cooled, the gas refrigerant would quickly become a liquid again.

Here’s how it really works. There is a component called an evaporator or cooling coil mounted inside the dashboard. The evaporator has liquid refrigerant flowing through it & its very cold ( on the surface about 2 degree C ). An electrical blower or fan is used to draw the hot air in the cabin onto the evaporator. The heat is absorbed by the cold refrigerant & what comes out from the evaporator is cold air.

The heat converts the liquid refrigerant into gas & it is moved by the compressor towards another component called a condenser. Cooler air from outside the car is drawn in by the forward movement of the car & the engine cooling fan. The condenser is usually at a temp. of 60 degree C. When the cool air from outside the car flows through the condenser, it cools the refrigerant, which is in gaseous state inside the condenser & it changes state to liquid again. This time the compressor will push this liquid refrigerant back into the evaporator & the cycle goes on over & over again in a split second.

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Cheers!

David