How Does Air Conditioning Work?
Air conditioners and refrigerators work in similar ways. An air conditioner is basically just a refrigerator without the large insulated box. An air conditioner uses the evaporation of a refrigerant, like Freon, to provide cooling.
Air conditioners use chemicals that easily convert the gas Freon to a liquid and back to a gas again. Freon is used to transfer heat from the air inside of a home to the outside air. An air conditioning unit has three main parts. The parts are a compressor, a condenser and an evaporator.
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Cooling With a Forced Air System
Most central air conditioners are connected to a home's forced-air distribution system. The same motor, blower, and ductwork that are used for heating are used to deliver cool air from the air conditioning system. When a central air conditioner is operating, hot air inside the house flows to the furnace through the return-air duct. The hot air is moved by the blower across the cooled evaporator coil in the air-filled space in the furnace and is then delivered through ducts to cool the house (see below).
The Freon gets to the compressor as a cool, low-pressure gas. The compressor squeezes the Freon, which packs the molecules of the Freon closer together. The closer the molecules are together, the higher its energy and its temperature.
The Freon leaves the compressor as a hot, high-pressure gas and flows into the condenser. If you looked at the air conditioner part outside a house, look for the part that has metal fins all around. The fins act just like a radiator in a car and help the heat go away, or disperse, more quickly.
When Freon exits the condenser, its temperature is cooler and it has changed from a gas to a liquid due to the high pressure. The liquid goes into the evaporator through a very tiny, narrow hole. The liquid's pressure drops on the other side. When it does it begins to evaporate into a gas. Freon extracts heat from the air around it as it changes to gas and evaporates. The heat in the air is needed to separate the molecules of Freon from a liquid to a gas. To help in exchanging the thermal energy with the air surrounding it the evaporator also has metal fins.
By the time the Freon leaves the evaporator, it is a cool, low-pressure gas. It then returns to the compressor to begin its trip all over again. A fan that circulates the air inside the house is connected to the evaporator and blows across the evaporator fins.
There is a vent near the ceiling where hot air is sucked into the air conditioner and goes down ducts. The hot air is used to cool the gas in the evaporator. As the heat is removed from the air, the air is cooled. It is then blown into the house through other ducts usually at the floor level.
This continues over and over and over until the room reaches the temperature you want the room cooled to. The thermostat senses that the temperature has reached the right setting and turns off the air conditioner. As the room warms up, the thermostat turns the air conditioner back on until the room reaches the temperature.
Basic Central Air Conditioning Maintenance
Both the evaporator and the condenser are sealed in a central air conditioning unit. Therefore, a professional service person should be called for any maintenance other than routine cleaning. Central air conditioners should be professionally inspected and adjusted before the beginning of every cooling season. While there aren't many repairs you can make yourself, there are some maintenance procedures you can follow to keep your system operating at peak efficiency.
The evaporator for the central air system is located directly above the furnace in an air-filled space, or plenum. The evaporator may not be accessible, but if it is, it should be cleaned once a year. If the plenum has foil-wrapped insulation at its front, you can clean the evaporator; if the plenum is a sealed sheet metal box, don't try to open it. You should have these tools on hand to clean the evaporator: a screwdriver to remove the access plate, a stiff brush to clean the entire evaporator, a large hand mirror to see what you are doing, household bleach to clean the tray below the evaporator, and wire to open the drainage hole from the tray.
During the fall and winter, outside condenser units should be protected from the elements to prevent leaf blockage and ice damage. Cover the condenser unit with a commercial condenser cover made to fit the shape of the unit or use heavy plastic sheeting secured with sturdy cord.
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