Why Is My AC Unit Buzzing Every Few Minutes?

Q: My AC unit is buzzing every few minutes, and it’s driving me crazy! What’s wrong, and is there a way I can fix it? Or do I need to call in a professional? 

A: When an AC unit is working properly, you’ll hear it kick on when it’s time to run and then a low hum while it runs and cools the home. But if something isn’t right with the unit, you may hear the AC buzzing every few minutes. This air conditioner buzzing is not only annoying, but it’s also a sign that something is loose or malfunctioning. This is particularly true if the buzzing is accompanied by other issues such as the unit not blowing cold air or the fan not spinning. 

HVAC systems typically last up to 25 years with proper servicing and maintenance, but failure to repair issues promptly may significantly shorten that lifespan. Hiring one of the best HVAC companies (such as One Hour Heating & Air Conditioning or Aire Serv) can help get your AC back to working order as quickly as possible.

1. Loose panels could be causing the AC to make a buzzing noise when it is turned on.

If your AC unit is buzzing every few minutes, it may be loose panels or bolts on the unit. Jerad Adams, director of product management at Friedrich Air Conditioning, an AC manufacturer based in San Antonio, Texas, says, “Loose panel noise is easily identified—you’ll hear the clatter when the system is running.” To determine if this is the issue, check the panels and bolts to make sure they’re secure. You can do this by pressing gently on the panel while the unit is buzzing to see if the buzzing stops. If it does, this is the one situation where it’s possible to remedy the buzzing noise without paying AC repair costs.

According to Adams, this loud air conditioner issue can be “easily remedied with a nut driver.” Determine which panels are loose and tighten the bolts around the panel. If there are missing bolts, these will need to be replaced.

2. If the unit’s contactor has worn down, it may cause inconsistencies in the power supply, which can result in a buzzing sound.

The AC unit’s contactor is an electrical component responsible for initiating the flow of electricity when the AC turns on. When the AC is turned on, the contactor acts as a drawbridge, sending the electrical current between two points. Melanie Powers, president at Goodberlet Home Services, a plumbing, HVAC, electrical, and construction company based in Kankakee, Illinois, says that the AC unit buzzing “might be due to insufficient current from the control source to engage the electromagnetic coil, insufficient voltage supply to the coil, or dirt or debris buildup on the active components.” Those comfortable with electrical work may be able to “replace it with caution,” she says, but calling a professional is probably the best bet.

3. Problems with the compressor can lead to a buzzing noise from the outdoor part of the unit as well as warm or weak airflow in the home.

The compressor is a main component of the AC and is responsible for cooling the refrigerant. A noisy air conditioner compressor can make a buzzing or humming noise, and you may also notice that the AC is not blowing cold air through the vents. The circuit breaker could also trip due to the increased power it takes for the compressor to run if it’s overheating. If this happens, one of the first signs you’ll notice will be the outside AC unit not turning on.

According to Powers, an AC compressor making noise could be because “it might be struggling to start, it could be due to a refrigerant leak, or it could be from high pressure that is built up in the compressor.” She encourages homeowners to call a professional to fix this issue. A new AC compressor costs between $800 and $2,000.

4. Condenser fan motors tend to wear out over time. When this happens the blades will stop turning and the motor may buzz or squeal.

When your AC turns on, the condenser fan on the top of the unit runs in order to remove the heat from the refrigerant. If the motor is worn out, the blades will stop turning, causing the motor to buzz or squeal. It will be clear if this is the case because the fan is easily visible from the top of the outside unit. Adams says that the condenser fan making a sound is “the most notable ‘uh-oh, something bad is about to happen’ audible indicator.” Because it’s so loud, he says that if you don’t notice it, “your neighbors will certainly let you know!”

If the AC unit’s fan isn’t spinning, it’s a good idea to turn the unit off until you can call in an HVAC company to check it out. Adams recommends calling an HVAC contractor as soon as possible to “replace the fan motor before it becomes an emergency no-cool air situation.” JJ Paulson, a home inspector and franchise owner with WIN Home Inspection in Chicago, Illinois, says that “this would not be the type of repair the average homeowner should attempt.” AC condenser replacement cost ranges from $300 to $5,000.

5. The capacitor is the part of the unit that prompts the AC to turn on. If it fails, it can lead to inconsistent cooling in addition to buzzing or humming sounds. 

The capacitor is responsible for actually turning the unit on and starting the motor. If the capacitor fails, the air conditioner sound you may hear is likely the result of the bad capacitor “causing the failure of both the fan motor and compressor,” says Paulson. A failing capacitor can also work sporadically, causing the unit to turn on and off at intervals. 

Replacing the AC capacitor costs around $180 on average and is a relatively quick job, but it is best left to the professionals. If you decide to DIY the job, Adams cautions that “it’s critically important to replace it with the correct part and ensure the system fully functions as it should post-repair.”

6. A refrigerant leak can cause the unit to freeze, and it may make a buzzing noise as it tries to continue working.

According to Powers, “With a refrigerant leak present, the hissing sound forms as refrigerant escapes through the leak.” If there’s a buildup of ice along with the buzzing AC noise, it’s likely that the AC unit has a refrigerant leak and the AC will need to be recharged. Recharging an AC must be done by a professional, and it entails removing old refrigerant from the system, fixing the leak, and adding new refrigerant. An AC recharge costs between $200 and $500.

7. In some cases the issue may be electrical, which could potentially become a fire hazard if left unaddressed. 

An air conditioner is a complex unit, and each element has to work in conjunction with all of the other elements in order to work correctly. Paulson says, “The issue with electrical is there are too many variables to narrow down a specific cause for a buzzing noise.” He explains that electrical issues that could result in the AC making noise include “a bad transformer which can be very loud…and compressor issues.” If the air conditioner is buzzing when turned off, this is another telltale sign that the problem is electrical. Electrical issues come with the potential for a fire and will need to be addressed by a professional.

8. If you can’t pinpoint the issue yourself or are uncomfortable with HVAC repairs, it’s a good idea to call an HVAC repair specialist.

If you’re running your AC, chances are it’s hot out and you don’t want to be without it for long. During the hot months, appliance repair services that service air conditioning systems often get busy. So if you notice a loud air conditioning unit, it’s best to call one of the best appliance repair companies or best AC installation companies as soon as possible so you can get on the schedule. These companies will be well versed in handling noisy air conditioner issues and can help with central air conditioning, through-the-wall air conditioners, mini split systems, and window air conditioners.

Adams encourages homeowners to contact an HVAC professional “at the first indication of any issue to prevent catastrophic damage to the unit.” HVAC contractors, he says, “are trained and experienced in identifying air conditioner ‘noises’ and are well equipped with proper tools to test the unit and its components as well as remedy the failure.” Paulson says he doesn’t recommend that homeowners attempt AC unit repairs either because “there are too many things that look easy to fix but could hurt or even kill you if you don’t know what you’re doing.” 

An air conditioner making buzzing noises is not a problem to ignore, although the cost of repair or replacement can be high. A full HVAC replacement cost can reach up to $12,500, but the good news is that a home warranty may cover HVAC repairs, which can reduce the up-front cost of repairs.