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Your Go-to Guide for Air Conditioning Noise

February 16, 2022

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“I have a noisy air conditioner.”

If you’re an AC technician, this must be one of the most frequent complaints you get from your customers.

This is despite the fact that most modern ACs are equipped with sound dampers, whose primary purpose is to keep the noise of the air conditioner to a bare minimum (25 decibels to 55 decibels).

Now, AC noise is a worrying problem that needs to be inspected before it turns into a permanent issue and turns costly. As you gain experience, you will be able to detect and zero in on the air conditioner problem just by listening to the noise.

But if you are relatively new to this industry, then it becomes a daunting task to identify the source of the noise. Even a detailed HVAC maintenance checklist cannot offer much help here.

This post is for all those technicians who find it tough to identify the source of the noise. We will take you through some of the most common types of air conditioning noise, along with their different causes.

Squealing or screeching noise

If the AC system is making a high decibel screeching or squealing noise, then it can be due to a variety of reasons like –

High pressure in the compressor unit

The first thing to find out is whether the noise is a high-pitched squealing noise. If yes, inspect the compressor immediately as it might be due to the development of high pressure in it. If you don’t repair this soon, the high pressure could even cause an explosion.

Faulty fan motor bearing

If the noise seems to be like that of a metal screeching (impact of one metal over another) when the device is turned ON, then the problem is mainly in the fan motor bearing. This sound indicates the need to replace the fan motor bearings.

Broken or worn-out belt

The squealing noise can also be caused if the belt is worn out or broken, especially if the air conditioner you are inspecting is centralized or ducted. The belt that connects the motor and the fan in older AC systems tends to wear out over time and requires replacing. Also, due to changes in humidity, the belt can expand and contract in the summer season, thus giving rise to some unpleasant noise.

Hissing sound

Here are the possible causes of hissing noises from the air-conditioner –

High compressor pressure

Again, you need to inspect the compressor for high pressure if you hear a hissing noise. You can verify this by checking if the noise slowly transforms from hissing to shrieking. This means the compressor in the outdoor unit has built-up pressure.

Leaking refrigerant

The refrigerant line is not immune to damage. As the AC system ages, the refrigerant lines deteriorate and trigger a refrigerant leak. This can cause a hissing sound in the AC system.

Grinding noise

Here’s what you need to check if you hear a grinding noise from your AC –

Motor failure

If the grinding sound is coming from the indoor unit of the AC, then the issue is mainly with the motor inside the unit. To prevent this issue, you should oil the motor during your regular maintenance checks at the beginning of the winter and summer seasons.

Compressor breakdown

If the grinding noise is coming from the outdoor unit, then the issue is mainly with the compressor. The pistons produce this grinding sound inside the defective compressor during operation. Replacing the compressor is recommended if this happens.

Clicking noise

If you hear a clicking sound during the beginning and the culmination of the cooling cycle, then the unit is fine. But if the clicking sound prevails and doesn’t go away, then it indicates the following problems:

Obstruction in the AC fan

If you are hearing a clicking sound from the outdoor unit, then you need to check the fan. An obstruction in the fan can create such noise. Regular maintenance of the AC system can prevent this issue.

Loss of charge in the capacitor

If there is no obstruction in the fan and the sound still originates from the outdoor unit, then it could be the capacitor losing its charge. The sound is a testament that the capacitor is incapable of powering the compressor.

Malfunctioning thermostat

If the clicking sound is quite loud, then it could be a problem with the thermostat. When the thermostat is working fine, you will hear a soft clicking sound. This is nothing but the sound of the relay sending power to the AC. If there is some wiring issue or the relay is broken, then the relay will send continuous power to the unit creating loud air conditioner noises.

Buzzing sound

Buzzing or humming noises from the air conditioner can be due to one of the following reasons –

Loose screws and parts

There are hundreds of parts in an air conditioner, and if one of them comes loose, then it can cause vibrations in the HVAC system during operation. This vibration, in turn, would produce a buzzing noise.

Loose wire

If you find that the buzzing noise is quite steady, then it can be due to an exposed or loose wire. This can cause an electrical problem or even sparks in the system if left unattended.

Freezing of parts

If the buzzing sound is coming from the indoor unit, then it can be due to the freezing of parts. This usually happens if the refrigerant is low or if the thermostat is set low.


Being an AC technician, it is not only important to understand the different components of an AC system but also to identify the different issues that can come up in these parts. This post can be a great start for you to identify the cause of different types of noises such as rattling noise, clicking noise, humming noise, etc. Think of yourself as the doctor and the AC as your patient. You find out the issue of the AC just by listening to the symptoms and curing it before the issue gets worse.

If you are an HVAC enthusiast interested in learning more HVAC business tips, keep an eye out for our HVAC blogs here.


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