Simple maintenance can greatly extend the life of a central air conditioner.

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Most of us take heating and cooling for granted. We expect our heating systems to keep us warm during the winter, and we depend on air-conditioning to keep us cool during the summer.

When the house is cold in winter or hot in summer, the natural reaction is to call for professional service. Fortunately, there is an alternative. You can cut service costs drastically and keep your heating and cooling systems working efficiently by doing some maintenance and quick fixes yourself. But first, it's important to know how the basics of how heating and cooling systems function.

How Heating and Cooling Systems Work

All climate-control devices or systems have three basic components: a source of warmed or cooled air, a means of distributing the air to the rooms being heated or cooled, and a control used to regulate the system (e.g., thermostat). The sources of warm air, such as a furnace, and cool air, such as an air conditioner, in a house often use the same distribution and control systems. If your house has central air conditioning, cool air probably flows through the same ducts that heat does and is regulated by the same thermostat. When a heating or cooling system malfunctions, any of these three basic components may be causing the problem.

Both heating and air conditioning work on the principle that heat always moves from a warm object to a cooler one, just as water flows from a higher to a lower level. Furnaces and heaters put heat into the air to make your home warmer; air conditioners remove heat to make your home cooler.

All heating and cooling units burn fuel. Air conditioners use electricity. Most home heating systems use gas or fuel oil; other systems use electricity. The heat pump -- an electrically powered climate control unit -- both heats and cools air. In summer it extracts heat from the air inside your home. In winter it pulls heat from the air outside and uses this heat to warm the air inside.

When the furnace is turned on, it consumes the fuel that powers it, whether it be gas, oil, or electricity. As fuel is burned, heat is produced and channeled to the living areas of your home through ducts, pipes, or wires and then is blown out of registers, radiators, or heating panels. Older systems use the heat they produce to heat water, which in turn heats the air in your home. These systems use a boiler to store and heat the water supply, which is then circulated as hot water through pipes embedded in the wall, floor, or ceiling.

When an air conditioner is turned on, electrical power is used to cool a gas in a coil to its liquid state. Warm air in your home is cooled by contact with the cooling coil, and this cooled air is channeled to the rooms of your home through ducts and out registers or -- in the case of room air conditioners -- directly from the unit itself.

In the next section, we'll review the different distribution systems used for heating and cooling the home.