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Why Is My AC Unit Making a Loud Buzzing Noise?

June 01, 2022

Air conditioners make some strange and scary noises! Regardless of what you’re hearing and how loud it is, don’t ignore your AC unit making new buzzing or vibrating noises—it could be a sign of a more serious problem. The experts at Patrick Riley can diagnose the cause of noises coming from your air conditioner and determine if repairs are needed. Below are some of the possible causes of loud buzzing noises inside HVAC systems that you may come across at home.

Would you rather speak with a technician right away? That’s what we are here for! Learn more about the AC repair services we offer, or keep reading to find out what our techs have learned about buzzing sounds coming from AC units.

AC Buzzing Noise #1: Electrical Issue

If your AC is making a loud buzzing noise, something might be wrong with your unit’s electrical setup

If an electrical current escapes the intended path and jumps between circuitry, it will create a phenomenon called electrical arcing. If your AC is experiencing arcing, it will likely make a buzzing noise. This is dangerous! Electrical arcing can cause serious bodily harm, hearing loss, and other injuries.

The solution: If you think you may have an electrical issue, turn off your AC system and contact an experienced technician. If you have an electrical issue, continuing to run your AC could cause the affected components to further deteriorate and lead to expensive repairs.

AC Buzzing Noise #2: Loose parts

Over time, parts of your AC unit can become loose and may start to rattle around when your AC system turns on. Depending on the part that’s loose, it can sound like your AC is buzzing, vibrating, or shaking.

With loose parts, a shaky AC can cause components to wear out faster than expected. The longer the shaking goes on, the more wear and tear the unit experiences, making part replacements more likely over time.

The solution: You’ll need the help of a tech. They should be able to quickly diagnose which part(s) are loose and repair them.

AC Buzzing Noise #3: Frozen Evaporator Coils

Evaporator coils are the curled components of your AC system where heat is transferred from your home’s air conditioner to refrigerant, which takes that heat outside and dumps it.

Refrigerant is very cold, but when a consistent flow of warm air from your home gets blown over the evaporator coils, it keeps them from freezing.

Warm air from your home is blown over cold evaporator coils, where heat is absorbed by refrigerant. The result is cool air that is then pumped back into your home.

However, if there isn’t enough warm air blowing over these cold evaporator coils (or refrigerant levels are low), these coils can freeze over, which can cause a sort of buzzing noise.

The solution: First, turn your AC system off. Running the AC system while your evaporator coils are frozen could damage it.

Step 1: Check your air filters. If your air filters are dirty and clogged, they could be blocking airflow to your evaporator coils, which can cause them to freeze over.

If your air filter looks like the one on the right, it's time to replace it.

Step 2: If you’ve checked your air filter and it’s clean, the next step is to check your return and supply vents. Are they open and unobstructed by items like furniture? If not, open them and remove any obstructions in front of them.

Step 3: If you’ve checked your air filter and vents, it’s time to call a technician. You likely have a refrigerant leak or a malfunctioning blower. Unfortunately, if either of these is your issue, a professional will have to assess and repair the problem.

AC Buzzing Noise #4: Damaged Isolation Feet

Your AC compressor is the “heart” of your cooling system. It sits in the outdoor unit of your AC hardware and pumps refrigerant to your home (while transferring heat out).

Inside the machine that’s outdoors, “isolation feet” hold the compressor in place.

A compressor held up by isolation feet inside the outdoor AC unit.

As your AC system begins to age, these “feet” can become damaged or start to break down, which can cause your compressor to become unstable. If your compressor is loose in your outdoor unit, it can cause your AC unit to make vibrating or buzzing noises when turned on.

The solution: Contact an AC technician. They should be able to tell if your compressor has worn out isolation feet and replace them if necessary.

Other Possible Reasons for AC Buzzing Noises:

If you’re still not sure what is producing a buzzing sound inside your air conditioner, there are other components that are known to produce audible noises when something is wrong:

  • Loose wiring
  • Failing or damaged condenser fan motor
  • Malfunctioning compressor
  • Contactor relay switch (switch in the outdoor unit)
  • Bad capacitor

All these issues are usually the result of normal wear and tear over time, but your Patrick Riley HVAC specialist should be able to restore peace and quiet to your system with replacement parts.

Not sure it’s a buzzing noise you’re hearing?

Sometimes it can be hard to tell exactly what kind of noise you’re hearing from your AC system.Here’s a list of other common noises you may hear from your AC system:

  • Banging: typically the result of a (very) loose or broken compressor
  • Hissing: most likely a refrigerant leak
  • Squealing: a bad compressor or damaged fan motor
  • Clicking: an electrical issue or debris in the blower motor

If you think the noise you’re hearing is more closely related to one of the above, you should contact a professional. They should be able to diagnose the problem and make any necessary repairs.

Still having issues with your AC? Hire Patrick Riley’s professional HVAC service techs.

If you’re still having issues with your AC system, our suggestion is to contact a Patrick Riley HVAC technician. You may not think your AC unit making a buzzing or vibrating noise is a big deal, but it could lead to some expensive repairs (or even a replacement) if not taken care of in a timely manner.

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By Ty Lindsay

Ty Lindsay is the Director of Field Operations at Patrick Riley | Isley’s and a 15-year veteran of the plumbing and HVAC trades. In 2010, Ty earned his Journeyman’s plumbing license. He became a Master Plumber five years later and earned his Journeyman HVAC technician’s license that same year. Ty’s breadth of knowledge in plumbing and HVAC includes both residential and commercial work. He’s been a loyal member of the Patrick Riley | Isley’s team since 2016.