Loud noises coming from a home AC unit are not normal—these units are designed to operate quietly, with noise barely above a whisper level for those inside the home. A loud knocking noise indicates something is wrong with your AC unit. In many cases, the problem is severe.
The most common causes of a loud knocking or banging noise are:
- A loose part in the AC compressor. This is the part that houses the outdoor unit. It could be its crankshaft, connecting rod, or piston pin. In many cases, this will require a compressor replacement; in others, the loose part needs to be tightened or replaced.
- An unbalanced blower. The blower is the “fan” unit, and it’s usually located indoors. If it’s unbalanced, it will create a banging or knocking noise as the fan spins.
- Other out-of-balance or loose parts. If the sound is more like a clanking, it could mean the compressor is loose or parts inside the blower unit are hitting each other. A professional needs to address these problems quickly, or they will get worse.
Remember, never open the compressor unit. It’s a sensitive and fragile unit meant to be serviced by a professional.
Other Causes of Knocking Sounds in the AC
Other types of noises, caused by different problems, can also sound similar to a knocking noise. For example:
- Rattling noises often involve a loose screw or other loose part rolling around in the unit, especially the blower. Sometimes, it could be a twig or other debris, especially if the sound originates from the outdoor unit.
- Chattering or clicking can be an electrical component. It should not make this noise except when AC is first starting up. If it is, it needs to be serviced and likely replaced.
- Rattling and squealing usually mean the fan is going bad, especially if it’s an outdoor fan.
What should I do if my AC is making knocking noises?
No matter what the cause is, these noises are serious. Start by turning off your AC unit—continuing to run it may cause further damage. If your AC’s user manual has troubleshooting suggestions, try them, but make sure the unit and power are off and that you follow all safety instructions. In most cases you will need to call a professional.
Never risk letting what could be a minor repair turn into a major AC emergency. Ambient Edge offers fast, reliable repairs with a 100% Satisfaction Guarantee. Let us get your AC up and running again—silent and problem-free. Call us, schedule online, or fill out the form below to speak with an AC pro today.
