My outdoor AC unit started making a loud rattling, buzzing, or grinding noise. It is much louder than normal.
A noisy outdoor AC unit usually indicates a mechanical problem that will get worse if ignored. A rattling noise is often caused by a loose part — check for loose screws on the unit cover, a loose fan blade, or debris like sticks and leaves that have fallen into the unit through the top grate. Turn off the unit and remove the top grate to inspect and clean out any debris. A buzzing noise indicates an electrical issue such as a failing contactor (the relay that turns the compressor on and off), a loose wiring connection, or a failing compressor motor. Do not ignore electrical buzzing as it can lead to a complete breakdown. A grinding or screeching noise means a bearing is failing, either in the fan motor or the compressor. This requires professional repair. A high-pitched screaming or hissing sound can indicate a refrigerant leak — turn off the system immediately as running with low refrigerant damages the compressor. For any persistent noise, turn off the system and call an HVAC technician. Running a failing component causes additional damage and increases the repair cost.
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