DIAGNOSIS: The compressor is in a protective lockout, usually from a previous overload, voltage issue, or internal fault.
FIX: Unplug the unit from the wall for 30 full minutes. This allows the compressor's internal thermal overload protector to reset. Plug into a dedicated outlet—no power strips or extension cords. Set to Cool, max temp (60°F), and highest fan speed. Wait 10 minutes. You should hear a distinct 'click' and hum as the compressor starts.
IF THAT DIDN'T WORK: If it still doesn't start, the compressor start capacitor is likely failed. This is a common failure point. It's a cylindrical component on the control board that can be tested and replaced by a technician.
HEADS UP: Repeated compressor lockouts often stem from low household voltage (like during a heatwave brownout). Using it on a dedicated circuit is critical for reliable starts.