Window (or through-the-wall) air conditioners are very simple appliances. They operate on the exact same principles as refrigerators, freezers and dehumidifiers.

Cooling:
All residential window air conditioners have a cooling system made up of four primary components: a compressor, an evaporator, a metering device and a condenser. Air conditioner cooling systems actually remove warmth from the air rather than cool the air.

Blower fan:
When the air conditioner is running, the circulating fan and compressor run simultaneously. The fan motor has two fan blades attached to it on either end. The fan blade inside the unit continually draws room air over the evaporator coils, which are cold. The fan blade outside the unit continually draws fresh outside air over the condenser coils, which are warm. Because the evaporator coils are cold, they cause moisture in the room to collect on them, much like a cup of ice water on a warm, humid day. As moisture increases, water drips down off the coils into the bottom pan of the air conditioner.

Thermostat control:
The thermostat on a window air conditioner senses air temperature entering the air conditioner. As the air entering the unit reaches the set temperature, the compressor turns off. The blower may continue to run depending on the selection chosen on the control panel. Digital thermostats work on a similar principle but display a more precise temperature.

Selector switches:
Air conditioner selector switches allow you to choose the fan speed. If "low cool" is chosen, for example, the fan runs at a slower speed. However, the compressor always runs at the same speed and offers the same cooling capacity regardless of fan speed.