If your central air conditioner will not cool but you can hear it running, it may just need to be cleaned. Whether or not this is the cause of the problem, it’s the first remedy to try. Plan to do this on a relatively warm day. The following are guidelines; always refer to your owner’s manual.
1Turn off the power to the AC unit. There is normally a shut-off or disconnect panel on the wall next to the outdoor compressor. Also shut off the air conditioner’s 240-volt circuit at the main electrical panel.
2Rake leaves and debris away from the outdoor condenser. Trim any bushes that might block airflow.
3Unscrew and remove protective grilles and the top cover or grille from the compressor. If the fan is attached to the grille, be careful not to pull any wires loose.
4Use a soft brush to clean dirt and debris from the fins, and then vacuum the fins with a brush attachment (taking care not to damage them).
5Use a hose and nozzle with a trigger grip to spray debris from the fins (from inside the unit). Protect the wiring and motor from water with plastic sheeting or a large plastic garbage bag. If your owner’s manual calls for lubricating the motor, do that now—but don’t over-lubricate.
6Reassemble the unit.
7To test it, turn the thermostat to OFF, reset the power at the disconnect next to the compressor and the main panel, and then set the thermostat to ON. To avoid straining an air conditioner’s compressor, wait at least five minutes between turning it off at the thermostat and turning it back on. Let it run for a few minutes, and then feel the two pipes that connect the condenser unit to the air handler (slide any insulation back). One should feel warm, the other cool.
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For more on maintenance tips, see Preparing Your Air Conditioner for Summer.