Why Is My Air Conditioner Making A Rattling Noise? [7 Causes & Solutions]

Under normal conditions, no matter which air conditioner you use, it will not make a rattling noise. That is to say, if your air conditioner begins to rattle, you should pay attention and try to fix it as soon as possible.

While an HVAC professional can usually handle the job, you may still want to know why your air conditioner is making a rattling noise.

In the sections that follow, I have summarized seven common causes and solutions to this problem. Once you understand these reasons, you can determine whether you can solve the problem on your own or if you need to contact a technician.

Let’s get started!

1. Loose screws and bolts 

When operating, many components, such as the compressor or the motor, will vibrate. After a long period of use, the screws and bolts will become loose.

When you turn on your machine, these small parts, along with the connected components, will make a rattling noise.

This problem is more likely to occur if your air conditioner has been running for an extended period of time.

How to fix it?

The noise can come from either the outdoor unit or the indoor unit. You can trace the source of the noise, cut off the power supply, and then use a screwdriver or anything similar to tighten the loose parts.

2. Debris stuck in the  condenser coils

We all love our garden. However, the trees and shrubs could become troublemakers for our air conditioning system. 

Because the outdoor unit cannot be completely sealed, leaves, twigs, flowers, rocks, or other particles can get into it.

When these particles get stuck between the condenser fins, they will constantly hit the fins around and make a rattling or knocking sound when the machine is on. They will even bend the fins and affect your AC’s performance.

How to fix it?

If you have repairing experience, you can turn off your device, disassemble the outdoor unit case, and use a vacuum or fin comb to get rid of the debris on the coil. For larger particles, you can remove them with your hand. 

However, if you don’t know how to deal with it, you should hire a professional.

3. Misaligned fan blades

The fan in an air conditioner, like the ceiling fan in your room, will accumulate dust and dirt over time, causing the fan blades to become unbalanced. Aside from that, improper installation will cause the blades to become misaligned.

When the misaligned blades spin, they will collide with the squirrel cage or the outdoor unit case, causing a loud rattling sound that you want to stop as soon as possible.

How to fix it?

Make a call to your local contractor. They will adjust the fan blades or replace the fan after the investigation. Before that, you can try to clean the fan blades if you have the expertise.

4. Defective fan motor

repair ac fan motor

Both the condenser fan and the blower fan have a motor. When either of these two motors fails, it can produce noises such as rattling.

How to fix it?

Mechanical wear and tear, a low lubricant level, or any electrical problems can all cause a fan motor to fail. Therefore, it is not something easy to identify and fix. You should make a call to an HVAC professional.

5. Failing compressor

Except for the fan motors, there is a motor inside the compressor can. When the AC compressor wears out, the motor can become loose and move around in the can, making a rattling noise. 

How to fix it?

The compressor is the heart of an air conditioner. When it fails, you have the option of replacing it or replacing the entire unit because a compressor is very expensive on its own.

In most cases, purchasing a new machine would be a sensible idea if the machine is not under warranty. 

6. Misaligned squirrel cage

The blower spins in a squirrel cage. When the squirrel cage is not installed properly, the fan blades will hit it and rattle. 

That is, the fan noise may not be caused by the blades, but by the cage that houses them.

How to fix it?

A certified HVAC technician will reposition the cage so that the fan blades no longer strike it.

7. Broken grille

If the grille or register is broken, it may shake and rattle when the air circulates in the house.

How to fix it?

You can try to repair it by repairing the grilles or registers’ hinges or latches. If you don’t want to bother, just hire a professional.

In conclusion

If you notice your air conditioner rattling, you should take immediate action to stop it. Otherwise, it may damage the entire system, necessitating an exorbitant repair bill.

The rattling noise could be caused by loose screws, nuts, or the compressor’s motor. Misaligned fan blades or a squirrel cage may also be at fault. This problem can also be caused by a rock or twig stuck in the condenser coil.

You can use this post as a troubleshooting guide and contact a professional if you are unsure what to do.

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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.