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How Does an Automotive Air Conditioning System Work?

How it Works:

Any system that lowers temperature operates in similar fashion.  First you take a gas, like Freon, and place it in a sealed system.  This Freon, or refrigerant, is then pressurized using a compressor.  As it's pressurized, it gets hot by absorbing the heat around it.  this hot gas is then circulated through a series of tubes that dissipates the heat.  Scientifically, the gas removes heat rather than adds cold, but that's a lesson in physics that doesn't really matter to us right now.  The gas can lose lots of its heat, in other words it gets really cold, when you reduce the pressure.  As it cools it becomes a liquid.  this is when you get cold air blowing on your sweaty forehead.  To use this system in a car, it needed very little adaptation from its early applications as a refrigeration device.  Since it was discovered that Freon (R-12) was harmful to the earth's Ozone layer, it's been phased out for automotive use, and replaced with R-134a refrigerant.  Some cars have not yet been converted from the old R-12 to R-134a, but this conversion can be done easily.

Components of Automotive Air Conditioning System:

Your A/C System is made up of a compressor, a condenser, an evaporator (or drier), refrigeration lines and a couple of sensors here and there.

  • Compressor:  This is the heart of the A/C System.  The compressor is what takes the refrigerant (the gas) and pressurizes it so it will cool the air.  It's run by an engine belt.  The compressor also has an electrically operated clutch that turns the compressor on and off as you demand more cool air.
  • Condenser:  The condenser is like a miniature radiator, usually mounted at the front of the vehicle right next to the bigger radiator.  Sometime the condenser will have its own electric cooling fan, too.  The hot, compressed air passes through the condenser and gets lots cooler.  As it cools, it becomes a liquid.
  • Evaporator:  The evaporator is another little radiator that does just the opposite task as the condenser.  As the super-cool liquid is passed through its tubes, air is forced through and gets really cold, right before it hits your face.  As it warms up again, the refrigerant starts turning back into a gas.
  • Thermal Expansion Valve:  You don't always want to freeze your toes off, so the A/C System has a valve that controls the flow of super-cool refrigerant to the evaporator.  This way you can regulate how cold the air blowing on you gets.  There are a few types of valves in use these days, but they all do the same thing.
  • Drier or Accumulator:  The drier, also known as the receiver-drier, is sort of the safety catch for your A/C System.  The compressor is only supposed to compress the gas form of your refrigerant.  However, there's always a chance that some liquid could make it back that far.  The drier catches this liquid before it can damage your compressor.  Since even the tiniest leak or carless installation can introduce water moisture to the system, the drier absorbs this chemically, using what's called a dessicant (similar to that packet of "DO NOT EAT" that comes with electronics).  The drier also has a filter that catches any gunk that might be in there.

That's pretty much the whole story!  Different systems also have sensors here and there to tell it pressure and temperatures, but they are specific to a make and model of vehicle.  Pretty cool huh?  If you need to do some work on your car or truck's A/C System, be sure to have a repair manual specific to your vehicle or to be safe, take the vehicle to a Certified A/C Technician.