Home air conditioners cool air by exchanging heat from the inside to the outside. We'll see here how the process works.
Air conditioners are one of those appliances most of us don't give a thought about until something goes wrong, which fortunately doesn't happen very often since fundamentally they're simple devices.
Home air conditioners, whether window units or whole house types are all basically the same. Probably the easiest way to think of how they work is to think of air conditioners as removing the heat from warm air, instead of a machine that produces cool air.
Air conditioners use a fan to blow inside air over a cold radiator, and a fan to blow outside air across a hot radiator that's also outside. We'll get to the real names used for these radiators in a moment but they work in the same way as an automobile radiator to exchange the thermal energy of the fluid inside with the surrounding air.
The fluid used as a heat exchange medium in modern air conditioners is called Freon. There are several types of Freon, but they all have the capacity to carry heat, and to change from a liquid to a gas and back again under very specific conditions of temperature and pressure.
Air conditioners rely on the property of any gas to get warmer as it's put under pressure, and to get cooler as the pressure in its container is reduced. As gas molecules get pushed closer together they collide with each other more and thus heat is given off, and vice versa.
An air conditioner has a closed loop of Freon that circulates constantly in tubing when the system is in full operation. A compressor (which works a lot like an air pump) is used to pressurize the Freon, which causes it to become a hot gas. The Freon flows from the compressor through the radiator which has outside air blowing across it. This radiator is called a condenser.
The Freon cools so much from the air flow that it turns from a gas into a liquid as it passes through the condenser, which is why we say the gas is condensed into a liquid. The Freon, still under pressure from the compressor, continues to flow through a tube from the condenser until it comes to the metering valve, sometimes called an expansion valve. This valve has a very narrow orifice, so when the Freon is on the other side of the valve, its pressure can drop a great deal. And so the Freon next enters the radiator that has inside air blowing across it.
That radiator is called an evaporator. When a liquid becomes a gas, the process is called evaporating. Keep in mind the Freon is in a closed system and that it evaporates within the tubing of the system, not to the air we breathe.
So as it passes through the tubing of the evaporator, the Freon absorbs warmth from the room air, which allows the Freon to evaporate thus cooling the metal fins of the evaporator. The room air, having been blown across the evaporator, is now much cooler. The Freon then goes from the evaporator to the compressor, to start the cycle over again.
This whole process continues until the air is the temperature to which the thermostat has been set. The thermostat then turns off the compressor so the room doesn't become cooler. The fan may or may not go off depending on how the controls are set. Most a/c units will keep the fan running to even out the temperature of the room. Some will provide the option to shut off the fan to reduce power consumption and noise.
There's not much more. The evaporator, being cold, will cause the warm and humid room air to lose moisture, leading to water buildup in the pan underneath. In the case of a window unit, the unit must be installed, generally with a slight tilt, so that the water will run to the outside, instead of dripping water in the room.
Air conditioners have a filter on their inside air intake to reduce the amount of dust getting onto the evaporator fins, which reduce their effectiveness by acting as an insulator. Filters must be cleaned or changed often to keep these appliances running properly, and dirt be cleaned from both the evaporator and condenser.
The electronics are relatively simple, providing for turning on and off the fan motor and compressor, sensing the temperature, and perhaps a remote control.
Now that you know how a home air conditioner cools the air, you also know how a car air conditioner, a dehumidifier, a refrigerator, and a freezer work - they all work on the same principle.
