Updated On

May 14, 2024

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    If your AC unit is making a loud buzzing noise, it’s usually a sign of an electrical issue — a failing motor, malfunctioning compressor, or a failing contactor or bad capacitor. Other problems, like frozen evaporator coils, can also cause buzzing sounds in your air conditioner. You should investigate and fix the source of the noise right away, as it could lead to large, expensive breakdowns down the road.

    If you’re interested in finding local HVAC repair technicians, you can fill out the following form:

    Get HVAC Estimates In Just 30 Seconds
    Then connect with local experts to get the held you need.

    What Are The Most Common Reasons For Your Air Conditioner Making Noise? 

    If your air conditioner is making an unusual sound, it indicates that something is not right with your system. Depending on the sound, you might be able to use it to figure out what is wrong with your system and potentially fix a noisy air conditioner.

    For more information on troubleshooting different AC sounds, check out this video:

    Squealing Sounds

    If your air conditioner is squealing when the fan, heater, or air conditioner is on, it is likely a misaligned or worn belt that connects the motor and blower. The sound may come and go from time to time, but it will be consistent for the most part.  

    If the squealing is coming from the indoor AC unit, it should be fine to run your air conditioner while you wait for an HVAC service technician to arrive. However, there is a possibility that the belt could break while you are using it. 

    A Screeching Sound 

    If you hear a screeching metal-on-metal sound that starts when you turn your air conditioner on, it is most likely the fan motor bearings in your condenser unit. When the bearings wear down, it causes the fan motor parts to grind together, which causes the sound. 

    Your air conditioner may continue to work for a while with lousy fan motor bearings, but using it that way will damage other parts that are more costly to repair. That is why it is always best to address HVAC troubles as soon as possible.

    A Loud Buzzing Noise

    A buzzing noise coming from your air conditioner can be a few things. The buzzing noise can be the system trying to power on a non-working component, or your unit could be frozen due to a refrigerant gas leak. 

    You should address any issues causing your air conditioner to make noise as soon as possible. If the problem is loose parts, you can probably continue using your AC while waiting for the AC repair professional to arrive. 

    Other sources of a buzzing sound might cause damage to your air conditioner if you continue to use it, or they may prevent your AC from working.

    Common Reasons for Your Air Conditioner Buzzing Noise

    If the buzzing noise is coming from your compressor, your outdoor unit is getting low voltage, you have a malfunctioning compressor, or the capacitor might be impaired. 

    Loose parts rubbing together in your HVAC system can cause a rattling or buzzing sound. You must fix any loose parts because they can damage other air conditioning components.

    Low levels of coolant will cause your unit to freeze. So, when you hear a buzzing sound, you can check your indoor and outdoor AC units for ice. 

    On the indoor unit, you may find ice on the evaporator coil. On the outside unit, ice on the refrigerant lines indicates low freon levels.

    If you suspect your refrigerant levels are low, you will need a licensed HVAC repair professional to recharge your system and fix any refrigerant leaks. 

    A broken contactor, failing capacitor, or wiring issues can all cause a buzzing noise. These components can breakdown from normal wear and tear. However, they could also get damaged from an improper voltage or even from the impact of a piece of debris.

    Humming Noises

    Like the other sounds your AC can make, humming noises can mean several things. Some are easy to fix, while others require the assistance of a licensed HVAC service technician. 

    If the issue is unbalanced isolation feet, you can use your air conditioner until you can schedule a visit from an air conditioning repair specialist. If it is an electrical issue, you should wait until the repair service diagnoses the problem. 

    Common Reasons for Your Air Conditioner Humming Noise

    The compressor in your outdoor air conditioning unit sits on isolation feet, which helps to dampen the sound your AC unit would otherwise make and prevent damage to your unit from the parts vibrating. 

    Over time, the rubber feet can get damaged or become unbalanced. There are repair kits you can buy to fix the isolation feet. 

    Electrical problems can cause different sounds. So, if you hear any strange noises from your air conditioner, the source could be any of these electrical components: 

    • A broken contactor relay switch
    • Improper voltage
    • Thermostat wiring problems
    • A broken or tripped circuit breaker
    • Electrical arcing
    • Broken electrical connections
    • Loose wiring
    • A low-voltage switch

    Low levels of coolant will cause your unit to freeze. So, when you hear a buzzing sound, you can check your indoor and outdoor AC units for ice. 

    On the indoor unit, you may find ice on the evaporator coil. On the outside unit, ice on the refrigerant lines indicates low freon levels.

    If you suspect your refrigerant levels are low, you will need a licensed HVAC repair professional to recharge your system and fix any refrigerant leaks. 

    A broken contactor can cause a buzzing noise. Contactors can go out, but the issue could also result from an improper voltage or even a piece of debris in the contactor. 


    Final Advice When Your AC Is Making A Loud Buzzing Noise

    It does not matter what is causing your air conditioner to make noise; you need to get it fixed as soon as possible.

    If it is something minor, it should not be very costly to repair, but leaving it could damage more expensive components. When in doubt, turn off your AC and contact a licensed HVAC technician to diagnose and resolve the problem

    Related: Why is My AC Making a Loud Noise When Starting or Shutting Off?

    Did You Know

    Your air conditioner may continue to work for a while with worn-out fan motor bearings, but using it that way will damage other parts that are more costly to repair.

    Use the form below to get price estimates from local HVAC providers:

    Get HVAC Estimates In Just 30 Seconds
    Then connect with local experts to get the held you need.

    Frequently Asked Questions

    Can I continue using my AC if it's making a buzzing sound?

    It depends on the cause of the buzzing noise — some can damage your AC unit further. So, I recommend turning it off and having an HVAC technician inspect it.


    How can I tell if the buzzing noise is coming from the indoor or outdoor unit?

    The easiest way to determine if the noise is coming from the indoor or outdoor unit is to stand next to each of them while the AC is running. You should be able to quickly tell the source.


    Is it expensive to repair an air conditioner that's making a buzzing noise?

    The repair cost to fix a buzzing noise depends on what’s causing it. For simple fixes like broken isolation feet or a failing contactor, you’ll likely pay under $200. However, if you need to replace your compressor, your bill could easily be more than $1,000 (unless its under warranty).


    Article Update Log
    5/14/2024
    Reviewed for accuracy, cost data, industry best practices, and expert advice by Jonathon Jachura.
    Editorial Contributors
    avatar for Alexis Bennett

    Alexis Bennett

    Contributor

    Alexis is a freelance writer with nearly a decade of experience covering the home services industry. She’s built considerable expertise in roofing, plumbing, and HVAC, as well as general construction and real estate matters. In her free time, Alexis enjoys coaching women’s golf. She lives in the Triad area of North Carolina.

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    photo of Jonathon Jachura

    Jonathon Jachura

    Contributor

    Jonathon Jachura is a two-time homeowner with hands-on experience with HVAC, gutters, plumbing, lawn care, pest control, and other aspects of owning a home. He is passionate about home maintenance and finding the best services. His main goal is to educate others with crisp, concise descriptions that any homeowner can use. Jon uses his strong technical background to create engaging, easy-to-read, and informative guides. He does most of his home and lawn projects himself but hires professional companies for the “big things.” He knows what goes into finding the best service providers and contractors. Jon studied mechanical engineering at Purdue University in Indiana and worked in the HVAC industry for 12 years. Between his various home improvement projects, he enjoys the outdoors, a good cup of coffee, and spending time with his family.

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