Air Conditioner Noise Measurement

Air conditioners help keep your home cool and comfortable during the summer months. However, they also produce loud running sounds when they’re on. A typical AC unit has a sound level ranging from 40–60 dB, which is comparable to a conversation or a running refrigerator. That said, the sound level depends on the type of air conditioner, the brand, and if it’s working normally.

If your AC unit is making abnormal sounds, like screeching, hissing, clunking, etc., noises, then it likely has a problem that you need to address and fix. Otherwise, it could cause additional damage and higher repair costs.

Why Air Conditioners Make Noise

Noise is unwanted sound and needs to be considered when designing HVAC equipment. Air conditioner noise is unavoidable, but it can be minimized by using insulators, rubber, and other noise-absorber materials. Good equipment design plays a big factor in the air conditioner noise emitted by the unit.

AC Components That Make Noise

In a mini-split system, the typical sources of noise are the condenser, which is located outside the house, and the evaporator, which is inside the house. The typical air-cooled condenser consists of the compressor, fan, coil, and expansion valve.

The compressor emits the highest sound pressure, and the sound pressure increases over time due to the wearing off of the vibration pads that are used to mount the compressor to the metal casing. Other factors include the wearing off of the components in the compressor, such as the motor, valve, and other mechanical components.

There is not much you can do to a hermetic compressor, as you will not be able to access the internal mechanical parts. If the noise comes from the mounting problem, this can be solved otherwise, you will need to replace the compressor for good.

Sometimes, the noise can come from the leaves and other materials that block the fan blades from rotating properly, and you can reduce air conditioner noise by cleaning in or around the unit. Check also the bearings of the fan motor which can cause imbalance to the fan.

The indoor unit or evaporator consists of an electronic control, cooling coil, air filters, and blower. The noise usually comes from the fan. Over time, dirt and other materials may block the movement of the fan blades and the air.

Hence, it is always a good practice to clean the air filters regularly. Internal parts that are not easily accessible should be cleaned by qualified technicians. Check also the bearings of the fan motor.

Sound Measurement

Sound waves are generated due to a change in air pressure and travel in all directions. The strength of the sound decreases with the distance from the source. The measurement of the sound pressure is usually taken about 3 feet from the source. For most people, the sound frequencies from 1kHz to 4kHz are the easiest to hear.

The typical sound pressure is as shown in the table below.

Typical Sound Pressure

The human ear hears the same loudness for sound pressure even though with different decibels for different frequencies. For example, the loudness at 93dB(50 Hz) is the same as 87dB(5 kHz).

The measurement unit usually used is dBA instead of dB. The dBA unit means that the sound pressure is measured using a standard “A” filter that has been placed in the microphone. This filter decreases the amplitude of the low frequencies but lets the higher frequencies pass through. Hence, the sound pressure using a dBA scale for 93dB(50 Hz) is the same as 87dB(5 kHz), which is 87 dBA.

Example of Wall-Mounted Sound Level Specifications

When purchasing any air conditioner unit, make sure that you check the air conditioner noise level that is usually printed on the product specifications of the unit. Both the indoor and outdoor units will have these specifications. If not, you can always request from the technical personnel to provide you with the values.

An example of the noise level specifications of R410A Wall Mounted Inverter Single Split Systems from Mitsubishi Electric is shown in the table below. Take note that the higher the cooling capacity, the higher the noise level.

Common AC Noises You Shouldn’t Ignore

If your air conditioning system is running normally, it should only make a slow and steady hum, along with some slight clicking noises when it turns off and on. If you hear any of the below noises with your AC unit often, you should call a local HVAC tech for help.

Whoosing Noise

A whooshing noise that sounds like air rapidly escaping from your AC unit could be from a refrigerant leak. If you suspect a refrigerant leak, you need to call an HVAC professional ASAP to find the source of the leak, fix it, and recharge your AC unit. Refrigerant is bad for the environment and can also cause a variety of health issues.

Clanking Noise

Loud clanking and rattling noises are often from loose or broken components within the AC unit, such as the condenser fan blades, mounting bolts, or the compressor. These issues are often hard to diagnose on your own, so an HVAC contractor is the best option to resolve them.

Grinding Noise

Worn bearings in your air conditioner’s fan motors are usually the cause of grinding noises. During routine maintenance, HVAC techs will lubricate these moving parts to prevent this type of problem. If your AC unit has not been serviced in years, it definitely needs it soon.

Humming Noise

While a gentle humming noise is normal, a loud or unusual humming can indicate electrical issues, such as a failing capacitor or a problem with the motor’s wiring.

Hissing Noise

Refrigerant leaks can also make hissing noises. A leak will cause your air conditioner to be less efficient, making it struggle to cool your home. If you don’t address the leak, eventually, your AC unit won’t be able to cool your home at all.

Dripping Noise

Dripping noises inside your AC unit can be a sign of a clogged or broken condensate drain line, which can lead to water damage and mold growth if you don’t resolve it promptly.

Clicking Noise

Some light clicking sounds when the AC unit starts up or shuts down are normal. However, continuous clicking could mean you have a faulty thermostat, control board, or compressor relay switch.

Popping Noise

Popping and banging noises are often from thermal expansion or contraction of the ductwork due to temperature changes. While this is generally normal, excessive popping may mean you have an undersized duct system or poor insulation.

What Should You Do About Strange AC Noises?

If you hear any of these out-of-the-ordinary noises coming from your cooling system on a persistent basis, you should turn it off right away and hire an HVAC technician to inspect it. They will be able to find the source of the sound, diagnose the issue, and fix it. If you attempt to fix it yourself, you can risk damaging your AC unit more or seriously injuring yourself. That said, some issues like a clogged condensate drain line and dirty coils are easy DIY projects for most homeowners. Regular maintenance, including cleaning or replacing air filters, can help prevent some of these issues from occurring in the first place.

Final Thoughts

It’s entirely normal for your air conditioner to make noises while it is running. Typically, HVAC systems make a slight hum of around 40–60 dB when they’re on. However, if you notice odd sounds coming from it, like banging, clanking, screeching, dripping, or grinding noises, you should hire an HVAC company to investigate the source and fix it.