Although some central air conditioner repairs must be handled by a qualified air conditioning repair person, you can handle simple repairs and maintenance yourself. Following, you'll find guidance, based upon the symptoms.

Air conditioner doesn’t cool
A central air conditioner that runs but doesn’t cool may just need to be cleaned. Plan to do this on a relatively warm day. Follow the instructions in your owner’s manual.

1) Before you begin, turn off the power to the unit. There is normally a shut-off or disconnect panel on the house wall next to the outdoor compressor. Otherwise, shut off the air conditioner’s 240-volt circuit at the main electrical panel.

2) Rake leaves and debris away from the outdoor condenser.

3) Remove any protective grille or cover from the condenser’s fins.

4) Use a soft brush to clean dirt and debris from the fins, and then vacuum them with a brush attachment (be careful not to damage the fins).

5) Unscrew and lift the top grille off the unit, if possible. If the fan is attached to the grille, be careful not to pull any wires loose.

6) From inside the unit, hose down the fins (protect the wiring and motor with plastic sheeting). If your owner’s manual calls for lubricating the motor, do that now—but don't overlubricate.

7) Reassemble the unit.

8) To test it, turn the power on and set the thermostat to turn the unit on. Let it run for a few minutes, and then feel the two pipes that connect to the condenser unit (slide any insulation back). One should feel warm, the other cool. Otherwise, call an air-conditioning technician—the refrigerant may need to be recharged.

Important note: Avoid straining an air conditioner’s compressor by waiting at least five minutes between turning it off at the thermostat and turning it back on.

Air conditioner doesn’t turn on
If your central air conditioner doesn’t go on automatically:

1) Be sure the thermostat is set to “cool” and below the current temperature.

2) A central air conditioner should be on a dedicated 240-volt circuit; check the main electrical panel and any secondary circuit panels for a tripped breaker or blown fuse. If you find the problem here, reset the breaker or replace the fuse.

3) Make sure the furnace power switch is turned on and that the outdoor condenser’s power switch, mounted on the outdoor unit, hasn’t been shut off. Also, be sure the 240-volt disconnect next to the compressor (in a metal box, usually mounted on the house wall) hasn’t been shut off.

4) Turn off the power to the air conditioner and check the thermostat.

5) Remove the thermostat’s cover and unscrew the wire from the Y terminal.

6) Turn the power back on.

7) Holding the wire by its insulation ONLY, touch the bare end to the R terminal and hold it there for about two minutes. If the compressor kicks on, the thermostat is faulty; replace it or call an air-conditioning technician. If the compressor doesn’t go on when you hold the two wires together, turn the power back off and call a technician.

Major room temperature swings
When room temperatures swing more than about 3 degrees between when the air conditioner goes off and on again, it generally means that the heat pump isn’t cycling on often enough. See “Adjust Thermostat Heat Anticipator.”

Room temperature drops too low
When room temperature drops lower than the set temperature on the thermostat, it usually means that the thermostat is improperly calibrated or installed where it doesn’t sense a proper sampling of room air.

Air handler squeals
Squealing sounds from a forced-air heat pump generally occur when the belt that connects the motor to the fan slips. If the blower is making a grinding noise, shut off the unit and call a heat pump repair technician—the motor's bearings are probably shot.

In most cases, the belt is improperly aligned or worn and needs replacement. Refer to your owner’s manual.

This job involves removing the access panel, loosening a couple of bolts that hold the blower motor at the proper tension, and realigning or adjusting the belt. In many cases, it’s a good idea to remove it and buy a replacement.

When reinstalling the belt, be careful not to overtighten it as this can wear out the motor bearings.

Water pools next to air conditioner
Air conditioners and high-efficiency combustion furnaces create significant condensation, which exits through a plastic drain tube. This should go into a floor drain or be carried away by a small “condensate pump.” If water is pooling at the base of the appliance, something may be blocking the water’s flow, or leaking, or the pump may not be working.

1) Look to see if one of the tubes is leaking. If it is, replace it.

2) Test the condensate pump by pouring water into its pan. If the pump doesn’t start, either it isn’t receiving power or it is broken. Be sure that it’s plugged in and test the circuit. If it’s broken, either get it repaired or replace it.

3) If the pump runs but doesn’t empty the pan, the ball-like check valve just before the discharge tube is probably stuck. Unscrew the check valve, loosen the ball inside, and look for an obstruction.

If it appears that a condensation drain tube is clogged with algae, remove it if possible (you may have to cut it and replace it later with a coupling). Run a wire through it to clear it. To kill the algae, pour a dilute solution of bleach (1 part bleach to 16 parts water) through the pipe.

4) Ice may be blocking the tube. If this is the case, be sure the filter isn’t dirty. If the filter appears to be fine, the air conditioner’s refrigerant supply is probably low. This is when it’s time to call an air-conditioning technician.

Air ducts are noisy
Many heating/cooling ducts are metal so they conduct noise quite readily from the air-handling unit to your rooms. To break the conduction of sound, you can have a heating contractor insert flexible insulation ductwork between the heating/cooling system and the ductwork runs.

If you hear a pinging or popping sound coming from the ductwork, this may be caused by thermal expansion or by air blowing past a loose flap of metal. Track along the duct runs, listening for the sound. If you find it, make a small dent in the sheet metal to provide a more rigid surface that’s less likely to move as it heats and cools.