Air conditioning systems are a necessity to most people nowadays, but have you ever wondered how they work? Understanding this system may seem like a daunting task at first, but it is really quite simple once it’s broken down into its parts. Most basic air conditioners, whether automotive, or residential in home units, consist of 3 parts. The condenser and condenser fan, the evaporator and the evaporator fan, and the compressor. These pieces work in conjunction to force condensation and evaporation of the refrigerant being used.
The compressor is arguably t
he most important part of the whole setup. The compressor takes the gaseous refrigerant from the evaporator(to be touched on later), and compresses it to very high pressure gas. This rise in pressure causes the refrigerant to become very hot as it enters the condenser(if you know the ideal gas equation pV=nRT, this fact may make more sense). From the compressor, the refrigerant flows from to the condenser, which, as it's name implies, condenses the refrigerant to liquid form. (For a more in depth discussion on the ideal gas law, Ideal Gas Law, Enthalpy, Heat Capacity, Heats of Solution and Mixing (Aichemi Series F:Material and Energy Balances. Vol. 4
The condenser is a series of passages for the refrigeran
t to pass through attached to heatsink fins. These fins facilitate the cooling and eventual condensing of the refrigerant as air passes over them by way of the condenser fan. As the air flows accross the fins, heat is transferred from the fins, to the air, lowering the temperature of the refrigerant, cusing it to condense and liquify. At this point, you have high pressure, hot liquid refrigerant in the line. This condensing
and cooling is what creates the cooling potential of the system. It is analagous to dropping a weight from a cliff. In order to drop the weight, and harness some of the work done, you must bring the weight from a low point to the high point which you want to drop it from. From the condenser, the refrigerant flows to the expansion valve (aka orifice tube in autos) and then to the evaporator.
The Expansion Valve and Evaporator
Much like wind resistance regulates the speed of a dropping weight, the expansion valve controls the evaporation of refrigerant. Without this valve in place, no pressure gradient would be achieved. This is important because without this gradient, freon wouldn't evaporate, causing the evaporator, and thus, the air to get colder. Once through the expansion valve, the freon is in gaseos form, and at a much lower temperature because of this evaporation. Re
lating this to the ideal gas law, the pressure drops, while the rest of the variables remain the same, leaving only the temperature to sompensate, doing so by dropping. Just think of how cold you feel after getting out of the shower. It is because the water left on your skin basically sucks the heat energy from your body in an effort to evaporate. The heat of your skin is lost to the water, so you feel cold. Where the fan on the condensor works to manipulate the freon, the evaporator fan is in place to manipulate the air by pushing it past the cold evaporator, lowering the temperature of the air.
Once out of the evaporator, the refrigerant is mostly gas which is desireable since liquids are,
by definition incompressible. Some of the refrigerant, however, is actually in liquid form.This liquid an be harmful if it gets to the compressor, so a drier is used between the evaporator and the compressor. This drier is just a canister with inlet and outlet high in relation to the ground. As freon flows through, the less dense gaseous form remains high enough to pass right through. The liquid, on the other hand, is denser, thus it drops down to the bottom of the drier, where it remains until it evapoorates to gas and escapes.
It’s important to note, that according to the 2nd law of thermodynamics, the cold air does not actually make the hot air cooler, but the warm air in your house or car isn’t making the cold air from you’re A/C system warmer either. Think of it like this, the air around you is many, many particles moving about the room at random. The temperature is really a measure of the average energy of the movement of these particles. If you take a sample of air at lower average energy(lower temperature), and introduce it to a the more )energetic air, the movement of the higher temperature air molecules will collide with the lower temperature molecules, raising their energy levels, and thus temperature.