Never run an air-conditioning unit when the outside temperature is below 60°F. Coils may frost up, restricting airflow.

Wait at least five minutes before restarting a unit. This relieves stress on the compressor.

Always turn on power 24 hours before using a central air conditioner. This gives the unit time to separate the oil from the refrigerant before cool air is required.

Keep drapes and curtains away from window units.

Keep vegetation, grass clippings and leaves away from the condenser grille.

Remove window units in winter, or protect them with tight-fitting waterproof covers.

Once a month

Clean filters with dishwashing detergent, rinse thoroughly and let them dry before replacing. This allows a free airflow, reducing stress on the fan. It also keeps the coils clean, so heat can dissipate easily, leading to lower operating costs.

Twice a cooling season

Slide the chassis out, if possible, and lubricate the compressor fan; the oil ports are often hidden by caps or screws. Use five drops of SAE 20 nondetergent motor oil for a window unit and 10 drops for a central unit. (Some window units must be removed for oiling.) The sealed motors on newer units don't require extra oil.

Clear the drain hole in the chassis using a stiff wire. Add a capful of bleach to the tray or pan base or wherever water collects.

Once a year

Clean evaporator fins of bugs and debris, and straighten fins with a fin comb. These are available from refrigerator dealers, or call Sears Industrial Tools 800/776-8666 and ask for part 9-RB14401 ($10). If visible coils are dirty, coils within the unit probably are too. Take the unit apart and wipe the coils with a clean, damp rag. Use dish soap, which won't corrode metal. Finish by wiping the coils with a soap-free wet rag.

If your unit is solely an air conditioner, turn it off at the breaker in winter. Otherwise the compressor heater will try to keep the oil in the unit warm and ready for use.