How To Fix It

Why Is AC Mini Split Making Noise When Off? How To Troubleshoot It?

Hearing strange noises from your mini split AC can be alarming. It might require professional service, or the repair can be an easy DIY task. The first thing to do is to be familiar with why your mini split AC makes weird sounds, even when off.

An AC mini split is making noise when off because of electrical issues and loose electrical components. In addition, other potential causes include problems with the contactor relay switch, frozen unit, faulty condenser fan, and boiling refrigerant. 

The rest of this article will discuss why an AC mini split unit is noisy when off. More importantly, I’ll walk you through the potential solutions. Let’s get started.

1. There Are Electrical Issues in the Compressor

The compressor moves the refrigerant from the evaporator to the condenser coils. It ensures the refrigerant transforms into liquid or gas when necessary. While it can become noisy when the AC runs, it can produce audible sounds even when the unit isn’t operational. 

More so, the noise may not be coming from the compressor itself. Instead, it could be from the support springs. They could have reached the end of their functional life, and they need to be more balanced. Hence, they can bang against the compressor after shutting off the AC. 

How To Fix?

A quick solution to the problem is to check the compressor. Look for loose components that could dangle and move, even when the AC isn’t operational. In worst-case scenarios, you might need to replace the compressor. However, this is a job that you should leave to the professionals. 

2. There’s a Problem With the Contactor Relay Switch 

One component you’ll find in the outdoor unit of your mini split AC is the contactor. It’s a relay switch that powers the condenser and compressor. Mechanical and electrical failures can happen over time, making it noisy, even when the AC isn’t working. 

Power and amperage are affected when the contactor relay switch malfunctions. Hence, you can hear a buzzing sound. 

How To Fix?

The best solution is to replace the contactor relay switch. Find one that matches your mini split AC, especially regarding voltage. You’ll find three main types of contactor relay switches: 

  • Single pole 
  • Double pole 
  • Triple pole 

If you’re not sure how to replace the relay switch or what kind of switch you’ll need, it’s best to contact a professional for help.

3. There Are Loose Electrical Components in the Unit

Loose connections are challenging to spot because they hide inside the unit. Since they’re invisible to the naked eye, the best thing to do is to listen. If you can hear noise when the AC is off, it’s time that you address the problem. 

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More than just the annoying noise, loose electrical components can also be fire hazards. 86% of AC fires are from mechanical failures. More so, half of them are from short circuits. As such, it’s crucial to address the possible causes to minimize fire risks. 

How To Fix?

Open the central unit and visually inspect the electrical components. Ensure they’re secure and tight. Otherwise, use screws to tighten the connections or replace loose parts to eliminate noise and minimize fire hazards potentially. 

4. The AC Mini Split Unit Is Frozen 

Even in the middle of the sweltering summer heat, the outdoor unit of your mini split AC can freeze. It’s normal, but it can indicate a possible problem. An AC unit freezing up can be because of various issues, including the following: 

  • Low refrigerant level 
  • Poor airflow 
  • The blower fan isn’t working 
  • Condensate lines clogging 

Using the mini split AC for a long time can make it freeze. The latter can be further exacerbated by other problems, including those listed above. When it freezes, you can hear a buzzing sound.

How To Fix?

If the mini split AC is frozen, the best solution is to thaw. Unfreezing the AC can take anywhere from 1 to 24 hours, depending on the extent of the problem. If it doesn’t work, call a professional to address the issue. 

5. The AC Condenser Fan Isn’t Working 

The primary function of an AC condenser fan is to keep the condenser cool. It converts gas into a liquid, ensuring the AC works. Such is vital in keeping the system cool. Once it overheats, the cooling system can malfunction. 

Over time, dirt can also accumulate in the condenser fan. Small debris might be falling from an immobile fan, which can cause a buzzing noise when the mini split is making noise when off. 

How To Fix?

If the problem is with the condenser fan, inspecting and removing the debris is the best solution. Alternatively, cleaning is also recommended to restore full functionality. Instead of doing it yourself, it’s best to hire professional services. The professionals have the right tools, knowledge, and skills to do the job. 

The condenser fan isn’t the only component you must clean. Watch this short video to learn how to clean a mini split AC unit: 

6. The Refrigerant Is Boiling 

When boiling water or milk, the liquid continues to boil even after turning off the heat. The latter is because residual heat continues. And if you listen closely, you’ll hear a gurgling sound. This is something that can happen in a mini split AC unit. 

The AC also works by boiling. The refrigerant will boil once it’s in thermal contact with air and abstract heat from it. After which, it condenses, letting go of the heat outside. It sets up a strong refrigerant circulation after operating for several minutes, and it will continue even after switching off the unit, which is what generates noise.  

How To Fix?

Unfortunately, there’s no solution to this, as it’s part of the natural cooling process. However, this noise should only last for a short time, so it’s not something you’ll have to listen to for a long time. It can be audible, but it should be gone within a few minutes. 

Read: Why Mini Split Fan Runs Continuously?

7. The Condensate Pump Is Working

AC mini split unit noises aren’t always indicative of problems. At times, they’re part of the normal functioning of the cooling system. For example, such is the case with the condensate pump. It helps drain excess moisture and might continue to run even after shutting down the AC. 

How To Fix?

Like a boiling refrigerant, this is one thing that doesn’t require a solution. Instead, the best thing to do is to wait for the noise to subside. However, if the noise doesn’t seem to go away within a few minutes, it might be a different problem.

Read: Can A Mini Split Cool A Whole House?

8. The AC Mini Split Unit Isn’t Draining Properly 

When the AC mini split unit is noisy even when off, one of the possible issues is improper draining. There can be a plug in the condensate drain hose. 

Such happens if water pools on the drain pan and can’t drain correctly. It’s also possible when the drain hose or pipe is bent. It means that water can have difficulty getting out. Hence, it will have gurgling noises. 

How To Fix?

To fix a unit that’s not draining properly, one of the best solutions is to unlock the drain pipe. It allows proper flow through the hose, so there won’t be noise. Take the PVC cap off the drain pipe and use a wire brush to remove the clog in the drain pipe. 

9. There Are Animals in the Cooling System

Squirrels, mice, chipmunks, and possums are some animals that can be present in your cooling system. They can get inside the outdoor units and damage the AC components. Aside from such, they can also make weird and annoying noises as they wreak havoc. 

How To Fix?

To keep animals out of the unit, close any potential entry points. You should also inspect the unit regularly, ensuring the animals can’t pass through easily. You’ll need to clean the various components to remove dirt and debris animals leave behind, which can be stinky and even become health hazards. 


A mini split AC unit can be noisy even when it’s not working. The latter can be a problem with the components or as simple as a frozen unit. Cleaning the unit can solve the issue. In some instances, it needs repair and replacement, which is best handled by professionals.