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 are better understood if you think of them as devices that remove warmth from the air rather than cooling the air.
When the unit is running, the circulating fan and compressor are running simultaneously. The fan motor has two fan blades attached to it on either end. The fan blade on the inside part of the unit continually draws room air over the evaporator coils, which are cold. The fan blade on the outside part of 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. When the amount of moisture increases, it begins to drip down off of the coils into the bottom pan of the air conditioner.
The thermostat on a window air conditioner works by sensing the air temperature entering the air conditioner. As the air entering the unit reaches the set temperature it will cause the compressor to turn 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.
The air conditioner selector switches allow the user to choose the fan speed. The compressor always runs at the same speed regardless of the settings. If low cool is chosen, for example, the fan runs at a slower speed but the compressor still offers the same cooling capacity. There are other switches to control louver operation and other features on some units.
