* Is the thermostat set to "cool" and below the current room temperature? The compressor won't run unless the thermostat calls for cooling.
* Is the power on to the unit? Check the breaker box for a tripped breaker or a switch that might have been turned off. Also check the power cord to the unit itself.
* Is there power to the thermostat? A faulty thermostat can prevent the compressor from engaging. Try replacing the batteries if it's battery-powered.
* Are the air filters clean? Clogged filters restrict airflow, causing the system to shut down to prevent overheating.
* Is the condenser coil clean and free from debris? A dirty condenser coil reduces efficiency and can cause the compressor to malfunction or shut down.
* Is there a refrigerant leak? A low refrigerant level will prevent the compressor from working correctly. This requires professional attention.
* Is there a problem with the compressor itself? A faulty compressor will need to be replaced, and this is a job for an HVAC technician.
* Is the system experiencing a capacitor issue? The start capacitor helps the compressor motor start; a bad capacitor will prevent the compressor from turning on. This also requires professional diagnosis and repair.
If you've checked these and the compressor still isn't turning on, it's best to call a qualified HVAC technician to diagnose and repair the problem. Attempting to repair an AC unit yourself can be dangerous.
