Air Conditioner Makes a Banging Sound When It Turns On – What’s That?

Low humming noises are common in appliances like air conditioners. But on a hot afternoon, you might have turned on your air conditioner and heard a loud bang. What does this mean? Do you need to take the AC for repairs? After consulting with HVAC experts, here's what we've learned. 

A loud banging sound coming from your air conditioner usually results from a faulty part. It might be a loose nut, piston pin, or broken dampers. It might also indicate that you need to change your compressor entirely.

Banging noises from your AC should be taken seriously to avoid irreversible damage. Continue reading to learn the likely causes of this and other unusual air conditioner sounds. 

Technician repairing air conditioner - Air Conditioner Makes a Banging Sound When It Turns On - What's That

Banging Sound From Air Conditioner - What Does That Mean? 

Subject: Lowering the temperature in air conditioning unit for greener energy power consumption.

A loud banging noise coming from the air conditioner can indicate that one of the parts of the unit is faulty.

Most of the time, it results from the internal fan jamming against the HVAC cage. A small part might have also disconnected, then started disrupting the fan blades. These issues can cause banging sounds when you turn your AC on. 

When you hear this sound, the first step is to turn off the air conditioner and figure out which part is making the noise. Allowing your air conditioner to run after hearing a banging sound is risky as some of its parts might be damaged. 

Common Causes of Banging Sounds From Turning On AC

While banging sounds from AC can be due to several reasons, here are the most common: 

Damaged Air Compressor

This is an image of compressor.

Loud sounds when you turn on your AC can result from a damaged compressor, specifically the compressor motor, which is considered the most important part of the unit. Another indication that your compressor might be the culprit behind the sound is if your cooling system is malfunctioning.

The compressor is an integral part of any air conditioner. It works by using its gears and pistons to compress air or gas. The compressor makes sure that there is enough pressure in the air ducts to be used for cooling purposes. 

An AC compressor operates by expanding and contracting gas to create a flow of compressed air. This device has two chambers - one for intake and one for exhaust - with an exterior fan pulling in outside air at high velocity.

At the same time, an interior motor pushes out the compressed air from inside to outside. A compressor typically has three major components: a motor, a housing, and an impeller.  

Old or Broken Dampers

Dampers are usually made of metals, and a rusty damper can also be the reason for a banging sound when you turn on your AC. A damper controls how much air enters or leaves an area. For example, they can control airflow through ducts and openings in walls, ceilings, floors, and openings between rooms.

A damper usually has two or more positions: fully open, partially closed, fully closed. There is an opening for air to enter or leave in each position. When the blades of dampers are loose, it can cause a loud bang when you turn on your AC.  

Expanding Ducts

Ducts transport cold air from the outside to the inside. An air conditioner has two ducts: a supply duct and a return duct.

The supply duct is connected to the outdoor unit of an air conditioner, and it carries cool, fresh air into the inside of your home. The return duct is connected to the indoor unit, and it takes warm, stale air out of your home.

Loud sounds might result from the expansion and contraction of the duct due to a change in pressure or temperature. This happens mostly if your ducts are made of metal. 

How To Get Rid of Banging Sounds From Air Conditioner

Since the common causes of banging sounds have been explained, here are ways to fix them: 

Tighten Loose Nuts and Screws 

Loose screws are the most common cause of loud noises from the AC unit. Loud bangs, vibrations, and rattling sounds can be a result of parts moving around or against each other. They can cause a lot of damage if they are not tightened properly.

The best way to tighten loose screws is by using a wrench and a screwdriver. It takes some time, but it is worth the effort because it will save you from the stress of repairing broken parts. 

Clean Condenser Fins

Disassemble and Clean Air Conditioner Parts by high pressure water or air from nozzle or vacuum.

Air conditioners use fins to direct heat away from the AC. The fins are attached to the air-conditioner's condenser and are often the source of dust and debris. These can cause a lot of damage to the unit, so they need to be cleaned regularly.

While they don't directly cause the banging sounds, dirt accumulating on the condenser can further cause your unit to malfunction. 

Clean Fan Blades

Close-up of a blue exterior residential air conditioner condensor with a rusty black grill

Cleaning the fan blades is a very important step in keeping the air conditioner working properly and efficiently. The dirt and dust that gets on them can find their way to the coils and cause damage. 

Air conditioning fan blades are made from mostly plastic and metal. Be careful when touching the blades. Also, make sure you turn off power to your HVAC units before cleaning.

Lubricate Motors

The lubrication of the compressor motor is essential for its smooth and soundless operation. Proper lubrication prevents wear and tear on the motor, which will keep it running smoothly for a longer period with minimal maintenance. You can lubricate all the compartments close to the joints with SAE 10 oil.

When the compressor motor is not lubricated, it can cause screeching and banging sounds. This also results in damage to the bearings and gears, leading to premature failure of the compressor motor.

What Do Different Sounds From Air Conditioner Mean? 

Buzzing Sound 

The filter is likely clogged if your air conditioner produces a buzzing sound. The air filter helps to remove dust, dirt, and other particles from the air blown out of the unit.

When this filter gets clogged with debris, it becomes difficult for the unit to function properly and clean the air blown into your house. If you want to ensure that your air conditioner functions as efficiently as possible and keeps your home safe and healthy, then it’s important to change the filter regularly.

Squealing Sound 

Squealing sounds from your air conditioner are primarily because of fan or blower dysfunction.

The main function of an air conditioner blower and fan is to circulate the air in the room by pushing it through the vents. The blower pushes outside air into the room and pulls in warm, stale air from inside the house. The fan circulates this heated or cooled air around the room.

When a screw attaching the fan blade to the motor is loose, it can cause irritating squeaking sounds. This can also be a result of rusted or unlubricated blade joints. 

Humming Sound 

A low occasional humming sound coming from electronic devices is expected. But in air conditioners, high-pitched vibrations and humming sounds can indicate electrical malfunction. Other reasons include refrigerant piping or a loose fan. 

Electrical problems are a common issue with air conditioners. They may be caused by damaged connections, worn insulation, a faulty thermostat, or anything related to how electricity is delivered to the system.

An electrical problem in an air conditioner can cause a fire and lead to serious injury or death. If you experience any electrical problems, you should turn off the power to the unit and contact an HVAC professional.

Bubbling Sound 

An air conditioner drain line is a pipe that carries the water from your air conditioner to the outside of your home. When a drain line of an air conditioner is clogged, it can cause a bubbling sound when the AC is turned on. This issue can be fixed by unclogging the drain line.

To unclog an air conditioner drain, turn off the unit's power. Then, remove the unit's top panel and locate and remove any obstructions that are blocking the drain line.

After removing obstructions, clear out any debris accumulated in the unit's interior and replace the panel before turning on the power again.

How do I reduce sounds From air conditioners? 

While there are abnormal sounds from AC units, some units can be particularly noisy without being faulty. The use of noise-reducing barrier materials can help reduce the amount of noise produced by electronics like air conditioners.

Technician repairing air conditioner


Your air conditioner helps cool your home or office by using a refrigerant to extract heat from the surrounding environment. It works with the help of a compressor, condenser, and evaporator coil.

Damage or accumulation of dirt in any of these parts can lead to unusual sounds from your air conditioner. To avoid this, it's recommended that you clean and service your air conditioner regularly.

Check out these two insightful articles to learn more about how your AC functions. 

Air Conditioner Delayed Start - Why and How to Fix

How to Clean a Ductless Mini Split Air Conditioner

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