On a hot summer day an air conditioner can make the difference between heat prostration and comfort. So, it is wise to learn how to identify small problems that might cause an air conditioner to break down.

There are three basic types of equipment used for cooling:
1) a fan
2) a water cooler
3) a refrigeration-type cooler (an air conditioner)

And, there are two basic types of air conditioners:
1) those that mount in the window or wall and are used to cool a single space
2) central units that pump cool air to several spaces from a single location via a series of ducts.

This week's offering deals with central air conditioners. They are most often installed as two separate components ö one at the furnace and one outside the house. The component at the furnace is known as the coil unit and the outside one as the compressor or condenser. The two units are connected by copper tubing that contains refrigerant.

When the air conditioner is operating, the refrigerant is pumped from one unit to the other via the copper tubing. Window and wall-type units have both components in the same housing. When properly installed a central air conditioner does more than just provide comfort by cooling. Air conditioners also circulate and clean air by use of in-line filters. Dehumidifiers also can be added to an air conditioning system to help reduce humidity that causes damaging condensation.

An air conditioner is a simple machine. The most complex aspect is understanding how the refrigerant works. A refrigerant is a compound that gives off heat when in a gaseous state and that absorbs heat when it is compressed into a liquid state. When the refrigerant is in the cooling coils, it has been compressed and absorbs heat. When it leaves the coils it is changed to a gas and gives off heat. The fan motor in the furnace circulates air past the heat-absorbing coils in the coil case, and the freshly cooled air continues through the ducts and goes out wall, ceiling or floor openings to cool the house.

The outside unit contains a fan that blows air through a device called a condenser. The condenser looks and acts exactly like a car radiator. Instead of motor coolant, it is filled with refrigerant that has been pumped to it from the coil case. At this time the refrigerant is in a gaseous state and expels the heat it absorbed inside at the coil case.

There are quite a few moving parts in an air conditioner. Most important are the pumps and fans. They must all operate at once in order for a two-piece central air conditioning system to work. The electric circuit that controls the furnace fan normally is separate from the electric circuit that operates the condenser unit. This is important to know because it is common for a fuse to blow out at the condenser unit. When this happens, the furnace fan continues to operate and the air conditioner runs but supplies hot air.

You should be able to hear the fans running at both the inside and outside units. Never call a service person to repair an air conditioner until you have checked power everywhere inside and outside. You don't want to pay $75 or more to have a $2 dollar fuse changed. A noisy condenser can result from a fan blade hitting something, a loose access panel, or a motor going bad. If the fan is clear and the panels are secure, call a technician and have the motor checked. A loud rumble at the furnace end of the configuration also can mean a bad motor, but chances are the fan belt needs replacing.