Understanding A/C

Whether it’s refrigeration, room air-conditioning or automotive A/C, most cooling system use the same operating principles and share analogous parts. So to understand how an A/C system works (and how it can fail), we’ll first have to know its major parts and function.

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Under Pressure
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First up is the compressor, the heart of the system. Its job is - as you’ve guessed it - to compress the Freon and pump it around the AC system through connection of tubes.

A central drive shaft runs inside the compressor within a ring of piston and cylinder assembly. When the A/C is “on,” an electro-magnetic clutch engages a pulley (which takes power from the engine via belts) to turn the compressor’s shaft. The rotation of the shaft is converted to the side-to-side pumping motion of the parallel pistons using an eccentric disc fixed to the shaft which the said pistons are mechanically connected to. A thin metal plate with special cut-outs seal the cylinder and acts as a passive valve system, keeping the Freon flowing in the correct direction. Before you get cross-eyed with my incredibly rich detailing, let’s just follow the Freon to its next stop.

Once the Freon is compressed, it’s sent to the condenser which not only looks very much like a radiator but it’s also usually located in front of one. With the help of the engine’s radiator fans, the hot compressed Freon gets cooled in the condenser. The Freon remains relatively compressed but the cooling “condenses” it to liquid form (a process by which the name “condenser” has  subtly hinted on). Next stop: inside the cabin.

The condensed Freon needs to make a pit-stop first through a dryer before entering the tubing leading into the cabin. No, the dryer is not like the hefty appliance that makes your freshly washed clothes dry and toasty. It’s a small metal canister that contains desiccant beads not unlike those inside little packets that come with new shoes. The dryer strips the Freon of impurities and moisture that may have leeched in, an important step to keep ice crystals from clogging the system.

Following That Freon.

Now that the Freon has been filtered, it’s led to an expansion valve. The expansion valve is regulated by the thermostat, controlling the amount of condensed Freon entering the next sub-system. Once passed the valve, the Freon expands (again with the name hints) into a larger diameter tubing which lowers the Freon's temperature to freezing.


Now that the Freon has been primed for cooling action, the tubing carrying it enters the cabin’s airbox. The airbox contains the evaporator, a motorized cylindrical fan, and a heating radiator. The heating radiator is a system separate from the a/c (a topic for another article).

The fan draws air from the cabin. Air first passes through a filter, trapping particulate matter like dust and pollen, before going through the evaporator. The evaporator is the last heat-exchanging junction for the Freon. Heat from the incoming cabin air is absorbed through coils and fins, “boiling” away the Freon within. The vaporized Freon travels back to the compressor, taking with it the heat and completing the a/c cycle, while the end product, cool air, is created and blown back into the cabin. The cycle continues until the desired cabin temperature is reached.

Now that we have most of the parts terminology down, we can discuss the usual troubles that ail A/C systems… next time!