You should refer any serious central air-conditioner problems--such as a defective condenser or any problems with the refrigeration system, which are closed systems--to a trained technician. However, keeping the components clean helps prevent most common problems.

To clean the filter, remove it from the furnace or air handler (it's usually located inside or very near the air-inlet side). Replace a disposable filter or clean a reusable filter according to the manufacturer's directions.

Clean evaporator or condenser coils by removing access panels and brushing or vacuuming the coils--or use a garden sprayer filled with a mixture of water and detergent to spray from the inside out (be careful not to spray the electrical components). Rinse with a hose (again, avoid the electrical parts). In the process, take care not to bend the fins or damage the coils (though if you accidentally bend the fins, you can buy a comb made for straightening them). While cleaning the evaporator, check that the condenser drain is clean.

Cleaning the blower's fan blades will keep your air conditioner operating quietly. Tighten the mounting bolts and lubricate any oil cups according to the manufacturer's directions.