Why Is My Air Conditioner Making A Pulsating Noise? [4 Causes & Solutions Revealed]

Liz Yang

Air conditioners don’t often make pulsating noises, but it is so annoying when they do. These sound waves continue to emanate from the AC, making us agitated and concerned.

Usually, the pulsating noise in the air conditioner is caused by the resonance of compressor and refrigerant lines. Sometimes, the fan motor and some loose parts could also be to blame.

But why do these parts make a pulsing noise, and how do you fix it? If you are not tech-savvy, you may not have a clear idea about these questions. Don’t worry, I have got you covered!

Take a few minutes to read this post, and you’ll know exactly what to do.

1. AC outdoor unit condenser pad pulsating 

AC outdoor unit condenser pad pulsating

When the AC is operating, the compressor will shake and vibrate, producing a pulsating or humming sound, which is totally normal. To mitigate this noise and make sure the outdoor unit is placed in the level position, people often put a condenser pad under the unit.

However, some condenser pads can’t do the work perfectly. If the pad is made of plastic, the motion of the compressor can easily transform to it but can’t be subdued effectively.  That is to say, the whole pad or even the whole machine will resonate and make loud pulsating sounds.

What to do?

There are two ways to remedy this issue. First, you can install a vibrating pad under each corner of the outdoor unit so that the metal case of the outdoor unit will not rub against the pad anymore. But you should check them every few months in case they are not shifted.

Another way is to replace the condenser pad. You can purchase a wooden or concrete one to see if it can absorb more vibration. But the wooden one is prone to swelling since it is exposed to rain, whereas the concrete one is expensive to make. 

2. Refrigerant lines lack insulation

Refrigerant lines lack insulation

The refrigerant lines can make small motions when the air conditioning unit is working. For example, the expansion valve will open and close periodically.

If these lines get in contact with a hard surface, such as a wall, they will rub against it, producing a pulsating noise.

Usually, the HVAC expert will install sound-dampening insulation around it to avoid this problem. However, if the installer fails to do so or if the insulation deteriorates over time, you will be able to hear the noise.

Aside from that, if the lines continue to hit the hard surface, a refrigerant leak can occur. If you hear a hissing sound at the same time, it could be a sign that the refrigerant is leaking.

What to do?

If you have repair experience, you can reduce noise by adding some rubber or foam material to the lines.

However, if you are unsure whether there is a refrigerant leak or if the lines are difficult to access, you should contact a local contractor. They have the equipment to locate the leak, repair it, and recharge your air conditioner.

3. Defective fan motor

Both the condenser fan motor in the outdoor unit and the blower fan in the indoor unit can make a pulsating noise when defective. When it tries hard to turn the fan blades but can’t achieve it, a loud noise will arise inside the motor. 

What to do?

Many reasons can result in a faulty motor, including too much debris, lack of lubricant oil, and normal tear and wear. Some could be done by yourself, such as cleaning the motor and blades. Otherwise, you should hire an HVAC expert to do the task.

Please cut off the power supply and take safety precautions when trying to clean the motor.

In some cases, you may need to replace it with a new motor. The fan motor is inexpensive but you should pay for the labor cost, which could be costly. 

4. Loose blades or other parts

Many components in air conditioners are fixed by screws and nuts. Since these parts will continue to vibrate or shake while in use, they will become loose and emit unusual noises with time. 

For example, the wobbly and unbalanced fan blades can produce a pulsating noise when they spin. 

What to do?

Fortunately, this issue is easy to fix. If you can trace down the source of the noise, you can turn off the whole system and use a screwdriver to tighten the loose part. When it doesn’t work, you can call for a pro.

Sum up 

When your air conditioning system starts to emit a pulsating noise, you should exercise caution. 

While the compressor will make a pulsating and humming noise under normal circumstances, this sound should be low and steady.

When you hear the weird pulsating sound, you should take a look at the condenser pad under the outdoor unit. It may resonate with the machine. When the refrigerant line is not insulated, it can also give off a pulsating sound. 

At last, you can check the state of the fan motor and fan blades. Other loose parts could also be the culprit. 

Fortunately, all of these problems are easily resolved by an expert or by yourself. If you don’t have the expertise, you should call a certified technician.

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.