Why Is My Air Conditioner Making A Whistling Noise? [9 Causes & Solutions]

When you turn on the air conditioner after a long day of hard work, you may notice it makes a high-pitched whistling noise. Your air conditioning system should normally be quiet, and this noise indicates that something is wrong, and you must take action.

The reason your air conditioner makes a whistling noise can often boil down to the low airflow, which could be caused by the dirty filter, closed dampers, blocked vents, or too many closed doors.

That is to say, you can often solve this problem on your own.

I’ll explain why low airflow can cause whistles, then go over each cause and solution to this issue. However, some causes should be addressed by a qualified technician.

Without further ado, let’s dive in!

What causes the air conditioning to make a whistling noise & how to stop it?

As I mentioned earlier, low airflow is the root cause of the whistling noise.

This is due to the fact that the air conditioning system requires a certain amount of air to function, and it uses the blower to draw the air in. When the airflow is low, the blower speeds up to try to pull in more air, resulting in high pressure and a whistling sound in the return ductwork.

It can also occur in supply ductwork when something prevents cold air from entering the room.

So, if anything interferes with airflow, it could be the source of a whistling noise in your air conditioning system. To stop the noise, you must address the underlying causes.

1. Dirty air filters

dirty air filters

There are numerous invisible airborne particles that can endanger our health. They can be filtered out by the air filter, ensuring that the air we breathe is clean.

As more contaminants attach to the filter, it becomes clogged, restricting airflow and causing the whistling sound. A clogged filter can also cause AC to freeze, which should not be left unattended.

How to fix it?

Examine the air filters in each return vent and replace any that are dirty. It is recommended that the filter be cleaned or replaced at least once every three months. If you have pets, you should increase the frequency.

2. Large debris in ducts

dirty duct

Dust, dirt, and debris will enter the ductwork if the air filter is not working properly. As a result, simply cleaning the filter may not be enough to eliminate the noise. The debris inside the duct can also obstruct airflow. 

How to fix it?

Make a call to the certified HVAC company or expert and ask them to schedule a duct cleaning. Or you can try to clean it yourself.

3. Blocked return and supply air vents 

This occurs more frequently in return vents than in supply vents. Return vents are frequently found at the bottom of a hallway or staircase. As a result, people may ignore them and place large pieces of furniture or items in front of them.

How to fix it?

You can solve this problem by moving the items to other places.

4. Closed dampers

If you have a large house, you may have installed a few dampers in the HVAC system to prevent airflow to unused rooms and save energy.

However, if you close too many dampers, the airflow in your home will be restricted, resulting in a whistling noise.

How to fix it?

To silence the sound, locate and open the closed damper.

5. Closed doors

Closed doors can obstruct air circulation inside the home. Only through the gaps can air enter other rooms. This increases the fan’s workload because it can’t easily suck up enough air.

How to fix it?

Try opening all of your doors to see if the problem has been resolved.

6. Leaky or wrongly installed ductwork

The airflow could be affected by an imbalance of air pressure in the ductwork. Whistles can occur when the ducts are broken or the duct system is designed incorrectly.

If your HVAC system was recently installed, the culprit could be improperly installed ductwork, whereas an older system is more prone to leaks.

How to fix it?

You should ask the certified HVAC contractor to check the design or the leak of the ductwork and then repair it. 

7. Faulty blower

If the blower fails to function properly, it will lose or reduce its ability to draw in air. To compensate, the blower will work extremely hard, resulting in a high-pitched sound and overheating.

How to fix it?

Don’t try to replace the blower yourself. Ask an HVAC professional to do it for you.

8. Return grilles are too small

small air grilles

This is another cause that needs the assistance of a professional. When the grille is small, your AC will not get adequate airflow by any means. If you have a new house and a new system, but the whistling sound can’t stop, check if this is why.

How to fix it?

You need a technician to enlarge the return grilles in your house.

9. AC system is oversized

When the air conditioning system is too powerful, it can suck up too much air per unit of time. Since this will increase the air pressure in the ductwork, it can make a whistling noise.

It can also make the AC turn on and off repeatedly, and the room will stay humid even though the AC is on.

How to fix it?

Call your local certified company to calculate how large the system you need; unfortunately, you may need to replace your whole AC system.

How to prevent your AC from making a whistling noise again?

Now that you know how to stop your AC from whistling, let’s look at how to refrain from it in the future. 

Hire a trustworthy company to design and install the AC system for you

An improperly designed ductwork, a small grille, or a wrong-sized AC can cause low airflow. Fixing or replacing it could be extremely expensive. As a result, you should avoid these mistakes in the very beginning.

A certified heating and air conditioning contractor could do the work properly. You can ask your friends or neighbors for advice.

Regular maintenance

Because a clogged air filter and ducts could be the source of the whistling noise, you should clean the filter on a regular basis and have a professional perform maintenance.

It can also make sure your AC keeps in tip-top shape, which can cut down the cost of electricity bills. 

Keep the doors and dampers open

Many people are used to shutting doors and using dampers. Nonetheless, if you want your AC to work properly, you should keep them open.

Sum up

Low airflow can cause air conditioners to make a whistling noise. When cleaning is overdue, doors and dampers are closed, or furniture is placed incorrectly, a whistling sound may begin.

There are numerous other causes. This guide will help you troubleshoot the problem. You can usually solve the problem on your own.

About The Author

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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 dozens 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.

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