Air Conditioner Compressor Buzzing Noise: Causes and Fixes

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When an air conditioner is working optimally, your air conditioner should not make noise other than the low hum from the spinning fan on the outside unit. While the older AC versions would make all sorts of noises, modern HVAC units are fitted with sound-dampening technology reducing the noise to around 25-55 decibels, depending on the AC unit you have. For example, 25 decibels are equivalent to a whisper, while 55 decibels are equivalent to normal conversation at home.

Therefore, if your AC is making any weird noise, especially a buzzing noise, something wrong requires professional inspection and repair. Luckily these noises only indicate something is wrong, and earlier troubleshooting will help you avoid parts replacements.

The compressor no longer works effectively if it starts making a buzzing noise. There’s also a chance that the electrical voltage and amperage are not optimal. In such a case, contact a professional to determine if the compressor has already failed and to replace it.

Air Conditioner Buzzing Noise Causes

Air Conditioner Compressor Buzzing Noise

Besides the compressor, other factors could trigger a buzzing noise in the air conditioner. The buzzing noise sometimes indicates an electrical issue within the AC caused by the unit wearing down over time.

Typically, the noise you notice is an indicator of “electrical arcing,” an electric discharge that happens when electricity leaps between circuits.

The following electrical components could cause the vibration:

  • The contactor relay switch in the thermostat controls the low-voltage switch in the outdoor unit. It powers the compressor of the outdoor AC unit with high voltage.
  • Circuit Breakers
  • Condenser fan motor (the large fan in the outdoor unit). If the fan fails to spin when the fan in the indoor unit is operating, the motor could cause noise.
  • Any faulty electrical connections in the outdoor unit 

Even if the AC is efficiently cooling your home, operating is unsafe. Using the air conditioner in this condition could cause irreparable damage, leading to a costly repair.

1. AC Compressor Electrical Problems

One of the most common problems your air conditioner is producing a loud noise or, in other cases, humming noises is due to electrical problems. This often happens when the AC unit is off.

It’s a common problem in the older ACs, which use a contactor relay switch that works hand in hand with the thermostat to regulate cooling. In most cases, the low-voltage switch fails to start, resulting in loud buzzing noise that won’t stop regardless of whether your air conditioner is working.

A loud buzzing noise can indicate a serious electrical problem in other cases. As the AC cycles on and off, it creates vibrations that can loosen the electrical connections.  Loose electrical connections can result in shorts or arcing becoming a serious fire hazard.

I would highly advise you to contact a professional AC electrician to help deal with the electrical problems.

2. Faulty Condenser Fan Motor

As the name suggests, the condenser is responsible for condensing the refrigerant as part of the evaporator/condenser loop.

On the other hand, the fan motor helps move air across the condenser coil, and when it fails, you will notice that your home warms rather than cooling.

Clicking noise from the fan blades can result from blockage preventing the fan from moving. If the blower is working, but the fan won’t turn, you must investigate further. There could be an electrical issue with the fan motor, or it could be loose parts in the motor itself.

In other cases, the blades won’t turn, but the motor works fine. You will hear a loud whistling or humming sound as the motor struggles to rotate. In this case, switch off the AC and contact a qualified expert because you risk burning out the motor the longer you wait.

3.Frozen AC Unit

Restricted airflow or a refrigerant leak to the outdoor AC can result in freezing. Refrigerant leaks often result in ice buildup, which can dramatically affect the effectiveness of the outdoor unit.

A broken fan motor can also result in freezing, making the AC produce a humming noise as the unit struggles to run despite being unable to.

If you spot ice on your outdoor unit and at the same time are able to hear a buzzing noise, it’s highly recommended you switch off the air conditioner and let the outdoor unit thaw.

At the same time, inspect for the possible reasons why the outdoor unit froze. You could repair the problem DIY, especially if the outdoor unit hadn’t been cleaned for a while. However, refrigerant leaks need professionals, and I would highly recommend you contact a qualified technician.

After the unit has defrosted, you can start your air conditioner again and listen for the loud buzzing /humming sound.air compressor making buzzing noise

4. Loose Parts

Did you know that loose parts in your air conditioning unit can make a buzzing noise? Your air conditioner has many different parts connected by screws and bolts working together.

The vibrations from the compressor as well as the fan from the outdoor unit can cause these components to move out of place. While buzzing is a sign of loose parts, the surest telltale sign of loose parts is banging noises when you switch on your AC.

It’s important to note that small loose parts can also make humming noises or buzzing noises that worsen over time. Therefore, it’s highly recommended that you inspect the outdoor unit, the indoor blower, and the AC compressor to figure out the source of the noise before it worsens.

Loose parts can result in uneven wear and tear to various components on your AC, including the compressor resulting in expensive repairs and replacements in the future.

5. Faulty Isolation Foot

The air conditioner compressor is always mounted on the base of the air conditioner unit. The compressor sits on a rubber foot known as an isolation foot.

Over time and due to wear and tear, the rubber isolation foot wears out, causing the AC compressor to become unbalanced, causing a buzzing noise when operating.

The isolation foot can be easily removed without the need for a professional. All you need to do is cut the electricity supply to the outdoor unit while installing the rubber feet.

The installation process is much easier, especially when you install with the help of an extra hand since you’ll need to tilt the unit to install the antivibration pads.

6. Refrigerant Leak

Tiny holes or fractures in the coils cause a refrigerant leak. Due to the elevated pressure that occurs when coolant leaks through these holes, it generates a hissing sound. If the discharge is too much enough, the AC will produce a buzzing or even a gurgling sound.

Please turn off your air conditioner and disconnect it from the electricity source. If the leak is barely noticeable, you can try fixing it using sealant or adhesive. If an adhesive can’t repair the leak, you must contact an expert. After the problem with the leak is fixed, have your air conditioner serviced.

Signs of a refrigerant leak include:

  • Frost build-up on the evaporator coils.
  • Higher than usual interior humidity levels
  • Long cycles of cooling (the air conditioner is on for longer)
  • Increased electricity costs
  • Gurgling emanating from your air conditioner.

Using ultraviolet (UV) dye, a technician can identify a refrigerant leak. A technician will use fluorescent dye to locate the exact location of the leak in the air conditioning unit. Once it has circulated throughout the HVAC system, the technician will use a detection lamp to pinpoint the exact location.

7. Electrical Malfunctions

Sometimes, the buzzing noises from your air conditioner may result from electrical problems. This might indicate a dangling wire or a defective circuit board. If there is an electrical issue, the unit may function less efficiently and even pose a fire hazard.

If the buzzing noise results from electrical issues, contacting a professional AC repair technician is essential to help resolve the problem immediately. They will be able to do the necessary repairs.

Final Thoughts

No air conditioning system is ever silent. Even with the quietest air conditioner on the market, you will always hear a gentle buzz/hum sound when it blows cool air into your house. If you live in a generally noisy neighborhood, you may find the gentle hum from the air conditioner white noise soothing when you need a nap.

Loud buzzing, rattling, and other different sounds, on the other hand, are an indicator of something wrong with your AC.  It’s in most cases tempting to ignore these early warning signs, but fixing them as early as possible will save you lots of cash in repair costs.

I hope this guide has helped you pinpoint the exact causes of air conditioner compressor buzzing noise without breaking the bank. Remember that some fixes require a professional while others can be fixed DIY.


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