Why Is My Air Conditioner Making Noises When It’s Off? Myths Busted!

Air conditioners can make noises when it is working. The noise will usually stop when the AC is turned off. However, air conditioners can sometimes make noise when it’s off. 

If your AC is buzzing, humming, or making other loud noises after shutting off, and you have no clue about it, you have come to the right place.

In the following sections, I will look at the most common causes and solutions for these noises. Some strange noises are actually normal, which may surprise you.

Let’s jump into it right now! 

1. A damaged condensate pump – buzzing noise

If your indoor air conditioning unit makes a buzzing noise when it is off, there is likely something wrong with the condensate pump. 

A condensate pump is not standard on all air conditioners. However, if your indoor unit is in the basement or any underground room, one should be installed because the collected water cannot drain by gravity.

The pump is not something that is to break down, but when it becomes clogged or malfunctions, it can emit a loud buzzing sound.

Because the condensate will continue to flow from the condensate coil to the drain line for some time after the machine is turned off, you will continue to hear the noise.

See also: why is my AC making a buzzing noise?

What to do?

Rather than repairing it, your best bet is to replace it since those condensate pumps are inexpensive. You can get a solid one at around $60. 

If you don’t have the expertise, you should ask an HVAC expert to install it. Otherwise, after turning off the whole system and unplugging the pump, you can try to replace it yourself. It is not rocket science.

Remember to maintain it regularly if you don’t want the buzzing sound to come back soon.

2. Dampers are closing – banging noise

Many HVAC systems have dampers installed to control the airflow. If the damper is motorized, it will close or open automatically according to the temperature and airflow. 

If you hear a banging noise inside your home when the air conditioner is turned off, the closing damper could be to blame.

What to do?

Usually, the banging noise will stop once the damper is closed. Therefore, you don’t need to fix it. If you can’t withstand the noise, apply some soft foam self-adhesive weather-stripping tapes to the exhaust hood or replace the old damper with a quieter one.

3. AC fan is set to “ON” – low blowing noise

AC fab is set to On

Depending on your needs, you can set the AC fan on “Auto” or “ON.” 

If the AC fan (also known as a blower fan) is set to “ON,” it will continue to blow air after the AC has been turned off in order to promote air circulation and provide a more balanced room temperature. The air will continue to blow out through the vents, making a low and steady blowing noise.

What to do?

This noise is normal, and you don’t need to do anything.

4. AC fan is on “ON,” but the motor is damaged – loud humming noise

When the AC is turned off, it is normal to hear some blowing noises from the indoor blower fan. However, if the noise becomes a loud humming, you should pay attention.

The blower motor can fail due to a lack of lubricant oil, excessive dirt and dust, or mechanical tear and wear. Because the motor can still receive power, but the fan blades can’t spin smoothly, the blower will eventually make a humming noise.

See also: why is my AC making a humming noise?

What to do?

If the problem is caused by debris, turn off the power and attempt to clean the motor if it is accessible. In some cases, the issue can be resolved.

If this method fails, the motor may need to be replaced, which should be done by an HVAC professional.

5. Metal air ducts expanding and contracting – clicking noise

It’s possible that the noise you’re hearing is caused by the ducts to which the AC is connected.

When the air conditioner is turned off, the temperature and pressure in the duct change dramatically. Because the ducts are made of metal, they will expand and contract, producing a clicking sound.

See also: why is my AC making a clicking noise?

What to do?

Luckily, this is just a normal sound and will stop automatically after a while.

6. Split AC indoor unit case expanding and contracting – clicking noise

split ac make noise when off

If you have a split air conditioner, the indoor unit may make a clicking noise even when the AC is turned off.

This is due to the fact that the indoor unit case is made of plastic, which expands and contracts with temperature changes.

What to do?

It is a normal phenomenon. If you want to reduce the noise, don’t set the temperature too high or too low. 

Recap

Now that you’ve learned about the most common causes of an air conditioner making noises when it’s off. While humming or buzzing noises usually indicate costly repairs, clicking noises are frequently caused by normal expanding and contracting.

Aside from that, keep in mind that if you set the indoor blower to “ON,” it will continue to operate even if the AC is turned off; if you want to eliminate noise, set it to “Auto.”

When you notice any wired noises in your air conditioner, your best bet is to contact a local contractor. Don’t leave it unattended because it could end up damaging the entire system.

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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 a lot of products in person, like 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.