How Air Conditioning Works In A Car

Summer is fast approaching and as the temperatures increase, so does the frequency in which we use our cars’ air conditioning system. Have you ever wondered how the system actually works? Let us explain it to you.

Air conditioning ‘conditions’ the air, it cools it down and also reduces the moisture content or humidity. All air conditioners work the same way whether they’re installed in a building, or in a car. The fridge or freezer is in a way an air conditioner as well. Air conditioning is a field in it’s own right, but we’ll focus on the main points on a car’s air conditioning and the main parts used.

Many people don’t realise that turning on the air conditioning actually reduces the number of miles per gallon of your car. This is energy expended in removing the heat and moisture from the air in the car which consumes petrol because of the extra engine load.

Air conditioning’s main principles are evaporation and condensation, then compression and expansion.

Evaporation: Have you noticed that if you rub a little bit of surgical spirits on the back of your hand, it will then feel cold? It’s evaporation. It’s because the spirits on the back of your hand start to evaporate. As the spirit evaporates, it takes away heat from the surface of your skin.

Condensation: Have you ever noticed when someone walks in from the cold into a warm room, their glasses steam up? It’s condensation. The moist air of the warm room cools as it contacts the cold surface of the glasses and the air has less capacity to hold moisture, so it condenses into water on the glasses.

Heat of compression: Have you ever noticed when you pump a bicycle tyre with a hand pump, that the end of the pump gets hot? This is due to the energy that you have put into the air by pumping it has not just compressed it, but has also caused the air molecules to push closer together so giving off heat with a friction.

Compression: At some point all liquids with eventually become gasses. An example would be a can of deodorant – inside the can is liquid, but it’s a gas when it comes out and hits your underarm. The pressure inside the can is higher, so the propellant inside is liquid.

Cooling by Expansion: With the deodorant, you’ll notice how cold it feels, which is because the propellant has just expanded in volume quickly.

Those are the basic ideas that are easy enough to explain, but the bigger question is how this all fit into making your cars vents blow cold?

Hard tubing and flexible hoses connect all the components of the air conditioning in your car. Evaporation and condensation, expansion and compression are the physics of why it works. There are five main elements to the whole system; the compressor, condenser, receiver-dryer, expansion valve, and the Evaporator.

The fluid that flows around the entire system is the refrigerant. This can evaporate at a low temperature, and then condense again at a higher pressure. In the old days, R-12 was the refrigerant common used in all cars. It was widely available; however it was being blamed as a contributor to the hole in the earth’s ozone layer as it was a chlorofluorocarbon (CFC). These ingredients were then discontinued.

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