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Air conditioners work as follows. Cool air circulates through ducts of a forced air heating system. The evaporator coils are usually inside the main supply duct directly above the furnace's blower, which circulates the air. The compressor and condenser fan usually operate on a 240 volt circuit and the blower on a separate 120 or 240 volt circuit with the furnace. A thermostat controls the system.

A central air conditioner's cooling capacity is rated in BTUs per hour. As a general rule, you need 12,000 BTUs for 1,000 square feet of well-insulated space. However, window areas, sun exposure, climate and other factors can also effect the house's cooling needs.

If your air conditioning system fails to perform, there are some things that you might try before calling a repairman.

Gaining access to your unit

a.. Turn off the power to the outdoor unit and to the indoor blower before opening the unit.
b.. Remove the fan grill by loosening the cap nuts.
c.. Remove the coil guard by unscrewing the bolts and screws around the base. Lift off, being careful not to strike the fan.
d.. Other housing can be removed loosening screws on top and sides.
e.. To reach the controls, loosen the screws holding the access panel. However, on some units, controls are in a small box with a removable cover.
f.. Open the compressor junction box by prying away the clip with a screwdriver.

Here are some common problems
To tighten loose fan blades, use a wrench for the bolts and make sure fan rotates freely and doesn't wobble. You might need to apply a dash of thread-locking compound. If a blade is bent, you should replace the entire blade unit.

To service a faulty motor, record positions of the motor connections, unfasten leads and any clips holding them. Remove the fan, loosen motor bracket with a wrench and lift the motor free, pulling the leads with it.

Testing the contactor

The contactor starts the compressor and the condenser fan. Open the control panel and trace the wires to their sources. Check for loose or corroded connections. Clean any corrosion from the terminals with an automotive-point file and clean switch contacts with an electrical contact cleaner.

Evaporator drainage

In most units, a plastic pipe carries the water outdoors or to a floor drain. Because algae and bacteria can clog them pipe, backed up water can puddle causing rust or shorting the blower. To clear evaporator drain, remove the plastic tape holding trap to the elbow. It might be necessary to saw through the pipe at the elbow. Then flush trap with hose by pouring in one tablespoon of chlorine bleach. Reattach with new tape.

Hints to help you maintain a good working air conditioner

a.. Clean or replace air filter every month during the cooling season and don't run the unit with the filter removed
b.. To avoid damaging the compressor, don't operate the unit when it is below 6o degrees F outside.
c.. Lubricate fan motor yearly if it has oil ports. Use non-detergent, light weight SAE 20 oil by adding no more than ten drops per quart
d.. Before restarting your unit in the spring or after a long shutdown, restore the power to tha air conditioner for 24 hours first. This will produce the heat needed to separate the oil from the refrigerant in the compressor.

If you find such thins as refrigerant leak, a faulty compressor, clogged evaporator coils, a faulty transformer, or a faulty fan motor, contact an air conditioning repairman. You may also need to have the compressor professionally recharged if you find a refrigerant leak.