Not all homes have--or need--a central air conditioner system. Necessity or economics may dictate that you install smaller air conditioners in a bedroom, nursery, or other living area for cooling during the hottest days. Of course, the "hottest day" is when it decides to quit working! Here's how to fix it. If you do have central air conditioning, see the Central Air Conditioner Fix-It Guide .

How Does It Work?

Components of a typical room air conditioner.

A room air conditioner is an encased cooling unit for mounting in a window, through a wall, or as a console. It is designed for delivery of cool air to an enclosed space without ducts.

Here's how it works: Pressurized refrigerant flows through a room air conditioner, alternately in gas and liquid form. When the unit is on, the condenser pulls in refrigerant gas and pressurizes it, raising its temperature. The heated high-pressure gas travels to the condenser coils outdoors, where the fins distribute heat to the surrounding cooler air. The gas condenses into a liquid that travels indoors to the evaporator coils where, under reduced pressure, it vaporizes into a gas, absorbing heat from the room. The blower pulls room air through the air filter and across the evaporator coils, where it is cooled, then blown back into the room. It makes the room cooler by pulling the heat out of the air. The operation of the unit is controlled by a thermostat.

What Can Go Wrong?

With a little maintenance, a room air conditioner should function satisfactorily for many years. The electrical cord may fail. The filter may need to be replaced. The coils may be dirty and the fins bent. The unit may be noisy and it may drip water inside. Routine maintenance includes cleaning or replacing the filter monthly during the cooling season and a yearly lubrication of the fan motor (unless the motor is permanently sealed).