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ac makes humming noise

Why Is My Air Conditioner Making A Humming Noise & What To Do?

When the air conditioner is turned on, it produces a low, steady humming sound. When this sound becomes louder, it usually indicates that your air conditioner is malfunctioning.

The humming noise is often caused by a faulty condenser or blower fan. The capacitor and bent fin coils can also be blamed. There are other reasons as well.

I will walk you through the most common causes of the humming noise in AC and teach you what to do about it.

Let’s jump right into it!

Common causes of humming air conditioners

An AC system consists of various components. Many parts in an AC can make a humming noise when defective. Therefore, it is important to trace the source of the noise so that you can know how to deal with it.

1. A faulty condenser fan motor

faulty condenser fan motor

The condenser fan motor can become stuck due to a low lubricant level, dirty blades, or other factors. That is, the fan cannot spin.

The motor, however, will continue to receive power. It will attempt to spin but will be unable to do so. It will make a humming noise during this process.

What to do?

If you don’t have the expertise, you should make a call to the local contractor. For those who want to have a try and have the expertise, you can cut off the power supply and then use a screwdriver to remove any obstructions on the blades to see if the issue is mitigated.

If it doesn’t work, you will still need a professional’s assistance.

2. A faulty blower fan motor

Unlike the condenser fan, the blower fan is used to blow cold air into the room or house. However, it can be damaged for similar reasons.

When it is unable to spin smoothly, it may begin to make noise. If you hear a humming noise coming from the indoor unit, it could be the blower motor.

What to do?

Please do not attempt to do it yourself. You will need to hire a local HVAC contractor to replace it.

3. Bent fins

Particles can enter the outdoor and indoor units and settle on the evaporator or condenser coils. When the fins bend, it affects not only the performance of your machine but also produces a humming noise.

In most cases, your air conditioner will continue to function, but it may eventually overheat, causing damage to your entire system.

What to do?

After turning off the power, you can straighten the fins with a fin comb.

4. A malfunctioning capacitor

If your AC hums but does not turn on, the capacitor is most likely damaged. The capacitor functions as a large battery, providing the extra power required by the motor. When it fails, the fan cannot function properly and makes a noise.

What to do?

Fortunately, capacitors are inexpensive and simple to replace. Because it is still an electrical component, you should have a technician do it unless you have the expertise.

5. A defective contactor

The contactor is responsible for delivering power to the outdoor unit. When it receives a command from the thermostat or remote, the relay switch inside closes, allowing electricity to flow through.

When it is broken, the outdoor cannot receive power, but the contactor can, and thus produces a humming sound.

A damaged contactor can also make a clicking noise.

What to do?

Ask an HVAC expert to replace it if it is damaged.

6. Refrigerant lines are vibrating

If the refrigerant lines are not well-mounted or strapped, they can vibrate, causing a humming sound. It can also happen when the refrigerant level is low, or the expansion valve fails. As a result, it can happen with both brand-new and old models.

What to do?

It is illegal to recharge refrigerant because it can endanger your health and the environment. You should hire an HVAC professional to mount, strap, or repair the leaks in the refrigerant tubes.

7. Loose components

The components inside the AC can become loose over time. Depending on the construction of the component, it may produce various noises, like humming and knocking

What to do?

Your best bet is still to hire a professional, but if you can pinpoint the source of the humming, you can turn off the power supply and tighten the part with a screwdriver or similar tools.

As a side note, the humming noise is similar to a buzzing noise but has a lower frequency. If you want to know why your AC makes a buzzing noise, check here.

How to keep the humming noise in your AC from coming back?

Based on what we discussed above, you may notice that the main culprits of the problem are faulty electrical components.

If you want to reduce the occurrence of humming noise in your AC, you should schedule regular maintenance. In this way, the technician can carefully examine each part’s state, making sure your AC will be in tip-top shape. For example, they will clean out the particles caked on the coils or tighten the loose part. 


Air conditioners can make a variety of noises, and determining what causes them can be difficult.

If your air conditioner is humming, it is most likely due to a faulty electrical component, such as the condenser, motor, or blower. In most cases, you will need to hire a professional to repair it. If you try to fix it yourself and lack the necessary expertise, you will end up damaging your device.

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Liz Yang is the founder of Airsmartly. She has been working at home for a few years and realizes that the performance of the HVAC system plays such an important role in our life. She has tested more than 150 products in person, including humidifiers, air purifiers, dehumidifiers, and ACs, and wants to share tips about using or troubleshooting these products with you. Her uncle is an HVAC expert with over 30 years of experience in the field, and often offers assistance when she is unsure how to handle a situation. He is also in charge of reviewing the articles on this site.

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