Like central air conditioners, room air conditioners extract heat and moisture from the room air, cool and dehumidify it, and return the air to the room. A blower pulls warm room air through a filter.

The main difference between a room and a central air conditioner is that a room air conditioner is a single, self-contained unit with evaporator or cooling coils, a condenser, and refrigerant-filled tubing all in one box. Air conditioner units mount in a window or through an opening in a wall, since they need to expel hot air.

evaporator
A system of coils in a refrigeration (or air conditioning) system that, when filled with cold refrigerant, cools the air around it. On a refrigerator, the evaporator is the coil inside the unit; an air conditioner's evaporator is inside the plenum on the furnace or air-handler.

condenser
Part of a refrigeration (or air conditioning) system that pressurizes refrigerant to cool it by changing it from a vapor to a liquid. On a refrigerator, the condenser is the coil on the outside of the unit; an air conditioner's condenser is usually outside the house.