Why Is My Aircon Making A Knocking Noise

Air conditioners make a variety of noises while they operate. From whirring, clicking, and buzzing, these sounds are the by-product of the operating machinery that makes our air cold. However, when your aircon makes a disturbing banging or knocking noise during operation, you may want to call a technician ASAP.

The knocking noise that you’re hearing may be coming from your aircon’s blower fan and the condenser fan hitting some form of obstruction. More seriously, it could be the compressor malfunctioning. Unfortunately, this isn’t normal, and you should call a technician ASAP.

In this article, we will discuss why your aircon is making a banging or knocking noise, and what you can do to fix it.

Note: If you want to learn how an aircon works, we’ve written about it before. Go check it out!

Malfunctioning blower fan

Air intake panel and blower

The blower fan is located right behind the evaporator coil of the aircon (which is inside the air intake panel). It is just off to the side of the blower (louver) itself. This is the fan that distributes the cold air inside your room.

A malfunctioning blower fan is the most common cause of the knocking noise that is coming from your aircon.

If the sound is coming from inside your room, and if the wind being blown out of the air conditioner is weak, then this is probably the case.

There may be something obstructing the evaporator fan. Check if there are any foreign objects stuck inside the fan. Also, when poorly maintained, the evaporator can build up a thick layer of ice around it – and the fan may be hitting the frost.

It could also be because the blower wheel is bent out of shape and is hitting something which is causing the knocking sound.

The fix: if the fan is frozen over you can clean it yourself if you are confident with your abilities. You can also remove the foreign object yourself if you can. Otherwise, you can always call a technician in to do it for you.

If the issue is with the fan motor or the fan blade itself, a technician will have to replace these parts for you.

Malfunctioning condenser fan

Aircon condenser fan

The condenser fan is located at the back of the aircon. For split type air conditioners, this fan is located at the back of the outdoor unit. The purpose of this fan is to help dissipate the heat absorbed by the Freon as well as to transfer this heat to the outside environment.

If the knocking noise is coming from the back of the aircon (or outside your house if you have a split type model), then it may be the condenser fan that is causing the issue.

Since the condenser fan is located outside, it is susceptible to foreign objects getting inside it. The fan blades itself can also be bent if a foreign object somehow gets caught while it is spinning. These can cause the knocking noise you’re hearing from your aircon.

The fix: like the blower fan, you can remove the foreign object from the condenser fan if you are confident with your abilities. Otherwise, you can always call a technician in to do it for you.

If the issue is with the fan motor or the fan blade itself, a technician will have to replace these parts for you.

Compressor problems

Apart from these two usual suspects, the compressor itself can also make a squealing noise if it is malfunctioning. The compressor employs a rotor a crankshaft to circulate the Freon along the coils of the aircon. These parts may be the ones that are causing the knocking sound coming from the compressor.

Additionally, it could be a loose part inside the compressor if not the whole compressor itself has come loose from its housing.

While compressor issues are quite rare (relative to the blower fan and condenser fan problems), they shouldn’t be ruled out completely.

An issue with the compressor is problematic as the compressor is the “heart” of the aircon, and if there is any problem with it, it will mean expensive repairs on your side, or complete replacement of your aircon.

The best course of action is to have it diagnosed by a technician.

The fix: Honestly, don’t. Just replace your aircon altogether. Not only does the compressor cost as much half of the price you bought the aircon for, the labor cost is also significant owing to the complicated nature of the job.


In summary: the knocking noise your aircon makes is a serious matter that should be dealt with ASAP! Call a technician to properly diagnose your problem.



2 thoughts on “Why Is My Aircon Making A Knocking Noise”

  1. Hello, I am having a loud clicking sound coming from my indoor split unit AC from Carrier. Have you heard of this before?


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