Why is my air conditioner making noise? It this OK, or can it be dangerous? How do I fix AC that is making noise?
If an air conditioner runs smoothly, nobody notices it. If, however, an AC starts making noises, we are right to be alarmed. AC noises are not just a bothering to our ears and hearing; an air conditioner making loud noises spells nothing good for the unit itself.
In some cases, you can repair a loud air conditioner yourself. That’s the best-case scenario. The worst-case are costly repairs, or replacing a noise-generating air conditioner.
There are 10+ types of AC units making various kinds of undesired pulsating, buzzing, or even clacking noises. These noises come either from the compressor, fan, air handler, and so on. With ducted AC units or mini-splits, AC’s inside the unit could be making a loud noise, or the outdoor unit.
It is important to differentiate between a loud AC unit (normal operating noise levels) and an AC unit that started making noises (concerning noises).
We will go through all kinds of noises AC units are likely to make. We’ll look into what is causing the noise, what part of the AC is making the noise, and how to fix a noisy air conditioner.
With so many different kinds of HVAC ACs and noises, let’s use a structured approach. For every kind of noise (pulsating, buzzing, banging, rattling, humming, etc.), we shall specify:
- What type of AC usually makes those noises (mini-split, window, portable, central)?
- Where the noise is coming from (compressor, fan, indoor unit – air handler)?
- Provide real-life examples of noisy units.
- How to fix noisy air conditioners.
Be aware that, in general, we describe noises with these terms: “buzzing”, “rattling”, “whistling”, and so on. Different people might have another word for air conditioners making “rattling” or “whistling” noises. We use the most general terms, and hopefully, we will be on the same track through all 8 kinds of AC noises.
1. Air Conditioner Making Pulsating Noise (Vibrations)
Hearing a pulsating noise from your air conditioner is worth a note. You should detect the rhythmic high sound / low sound / high sound / low sound noise; your AC might even sound like a helicopter.
Example 1: Window air conditioner making pulsating noise.
Example 2: Mini-split’s outdoor unit is making a loud rhythmic noise.
Why does your AC pulsate? In almost all air conditioners making pulsating noise, the culprits are:
- Compressor; the primary source of pulsating noise.
- Refrigerant wires; the secondary source of pulsating noise.
Pulsating noise is usually generated by a vibrating AC compressor. AC compressor pulsating noise is a direct result of the AC compressor not being absolutely fixed. If it has just a bit of wiggle space, the forces that run the AC compressor will move it from side to side; the compressor will be vibrating.
The pulsating noise you hear is most probably the AC compressor hitting something. Alternatively, refrigerant wires might also be a cause of the air conditioner making loud pulsating noises. If they are too close to a wall, they might be vibrating and hitting the wall repeatedly, generating pulsating sound.
How to fix an AC making pulsating noise?
You have to stop the AC compressor vibrations. That means that you have to fix it in place. If you have a mini-split open the outdoor unit and check for the AC compressor (it like a bit like a car battery).
Check the platform the AC compressor is on; plastic platforms, for example, can crack and the AC compressor starts making pulsating noise. You can replace it with a wooden platform to dampen the vibrations and eliminate the pulsing noise. You can also create additional support that will stop the AC compressor from shaking; usually, small rubber isolation feet are used to dampen the vibrations and suppresses the pulsating sound.
In window AC units, remove the back panel (facing outdoors) to reach the AC compressor. Check if it’s vibrating, and fix it in place. Compressors will usually have small rubber isolation feet; if those are missing or damaged, the window AC will make pulsating noise.
You can use support – something as simple as underpinning it with a piece of wood – to stop it from shaking and generating pulsating noise – or tighten the screws that hold the compressor in place (in some cases they get loose after 10+ years of use).
If the refrigerant lines are making noise, try to wiggle them away from any hard things like walls. They can still be vibrating; the key is that they are not smashing against something. That would create the rhythmic pulsating noise.
2. Air Conditioner Making Loud Buzzing Noise (Compressor Problem)
AC unit buzzing every few minutes is not that uncommon AC noise problem. Some units like window AC can be making loud buzzing noises every now and then. Is AC buzzing noise something you need to worry about?
Yes; in almost all cases. Buzzing sound is one of the AC noises that the hardest to pinpoint. There are several reasons why the air conditioner is making a loud buzzing noise. We can categorize them as:
- AC compressor making a buzzing noise (malfunctioning contactor). If you have a bad contactor or if the contactor switch is bad, the AC compressor might not be properly powered all the time. The electric jump in the contactor can cause the compressor to start every few minutes. Air conditioner compressor buzzing noise is the most common reason why the AC unit is buzzing every few minutes.
- Vibrating compressor. If one or more isolating legs that hold the AC compressor in place are damaged, the compressor might be the root cause of the buzzing sound.
- Refrigerant leak. If the freon starts leaking out of the copper refrigerant lines, the AC unit will start freezing up. A whole range of problems will follow, including the distinctive buzzing sound coming from either indoor or outdoor units. Extra note: If you want to recharge the window AC unit with freon, make sure to first seal the leak before putting the refrigerant in.
- Capacitor causing the buzzing noise. A capacitor is used to bring power to the fan; if you have a bad capacitor, the power delivery won’t be continuous as it should be. Every now and then the capacitor might send a power surge to the fan, creating a characteristic AC buzzing sound in the indoor unit.
- Fan blades being out of balance. If a fan is damaged, it can generate a buzzing sound while rotating.
- Bonus: Cleaning a condenser coil might help.
As you can see, there is a wide range of reasons why an air conditioner is making a buzzing noise. Fortunately, you can fix most of them by replacing the parts that are causing the buzzing.
For example, you can replace the malfunctioning contractor and the compressor will again receive a continuous stream of electricity. Replacing the isolation legs or adding wooden support will fix the compressor. You can also replace the capacitor and buy a new fan; with a few technical skills, you can solve the AC making buzzing noise problems yourself.
The only exception is the refrigerant leak. Fixing refrigerant lines is not so easy to seal; some DIY enthusiasts can certainly do it, however. Most homeowners do choose professional HVAC help when the buzzing sound is caused by low levels of freon due to a leak.
3. Air Conditioner Rattling Noise (Loose Panel)
Rattling noise is a very specific sound, most often connected with detached panels.
A sound coming from the air conditioner is something like what the rattle state sounds. Quick up and down sound volume changes with high frequency.
Fortunately, if you hear a rattling noise coming from your air conditioner, you don’t have to worry; it’s probably nothing serious.
What might be causing the air conditioner to make a rattling noise?
There are 4 potential culprits, with the detached or loose panel being the primary one:
- Loose panel door. The primary source of rattling noise in AC units is the easiest one to fix. The panel or cabinet door is covered by a thin metal foil that bangs against the rest of the air conditioner if it’s not properly screwed in. All you have to do is just screw the panel and secure it. The rattling noise usually starts because a screw might be loose, or after repairs (if we don’t secure the cabinet doors well enough).
- Debris in the outdoor unit. If you have central air or mini-split AC, the cause of rattling noise might be debris in the outdoor unit. The outdoor unit is exposed to the environment; twigs, leaves, or even small animals like rats and birds can be found in those units. Rattling noise is a consequence of the fan hitting this debris. To fix the rattling noise, open the panels and remove all the debris you can find; run the AC again and see if that eliminated the rattling noise.
- Misaligned fan. If a portable air conditioner is generating rattling noise, it’s probably the problem with the fans (the blades are producing the vibrations that eventually lead to rattling noises). Most often, there is a misalignment of two fans; the blower fan in the air handler and the fan in the condenser coil. This anomaly will cause the unit to shake; including the panels. If the panels are not completely secure, this extra shaking might cause these panels to make an unnecessary rattling noise.
- Damaged motor. ACs use motors to propel the fan and provide power to the compressor. If the motors are damaged (old motor, worn-down parts), you may hear a rattling noise coming from the indoor or outdoor air conditioning unit. You have to be careful here; running a busted motor can damage your whole AC unit. The best thing is to replace the faulty motor; the rattling noise will go away.
As you can see, fixing the rattling noise is usually as simple as screwing tight some panel screws. Just be careful if you have a damaged motor; to get rid of the rattling noise in that situation, the most sensible thing is to replace the faulty motor.
4. Air Conditioner Whistling Noise (Low High-Pressure Airflow)
If you hear a high-pitching whistling noise coming off your air conditioner, the problem is most commonly a low return airflow.
Whistling noise is caused by the high air pressure in the air conditioner. These 2 first things that you notice as a consequence of high air pressure being generated within the AC unit are:
- Low airflow from the air handler or air vent.
- High-pitched whistling noise being generated by the air handler or air vent.
The real problem is usually the inflow airflow restrictions. Whistling noise is created due to restrictions in the ability of the air conditioner to suck in hot indoor air. This air is sucked into the air conditioner and run over cool evaporator coils; this cools down the air.
If not enough air is sucked into the air conditioner, the outflow airflow from the air handler will also be restricted. When this is happening, the air pressure inside the air conditioner is increasing. The high-pressure air is moving faster than it normally would, generating characteristics whistling noise. The swirling of air under higher pressure produces the high-pitch sound you can hear from your AC unit.
How do you fix a whistling air conditioner?
Restricted airflow can be caused by several occurrences that you can very easily fix:
- Cleaning or replacing air filters. Saturated air filters will let through less air; if you remove the dust on them or replace them completely, the airflow will increase, the air pressure inside the AC unit will normalize, and you will effectively eliminate the whistling sound coming from the air vents.
- Obstructed inflow vents. Portable or window AC units might produce a whistling sound if their air intake is blocked by a window, a couch, or some other furniture. The easiest way to fix a whistling sound from the AC is just to move the furniture or remove any blockage that is restricting the normal airflow.
- Limited ductwork. In ducted air conditioners, such as the central AC unit, the HVAC ducting must provide sufficient airflow to the air blower. If the ducts are too narrow, the limited airflow will increase the air pressure, and you will hear a whistling noise coming from your indoor AC unit. HVAC installers usually take care of the ductwork; they calculate the necessary crosssection of ducts to provide sufficient airflow to the AC unit. If they miscalculated, the result can be a whistling sound, and the fix is to either get an AC with lower airflow or expand the ducts (usually this means they need to be replaced).
If fixing these problems doesn’t eliminate the whistling sound the air conditioner is making, the alternative reason why the AC unit is whistling are the duct leaks.
Even if you have sufficient ducting, the leak in the HVAC duct system will reduce the airflow, and you will see the same whistling effect as with limited ductwork.
5. AC Clunk Noise (Loose Or Broken Parts)
If you hear clunk noise from your AC – clunk, clunk, clunk – the reason is usually that one or more parts are loose or broken.
Broken parts may include a failing motor, a damaged indoor fan, or, worst of all, the compressor itself.
To fix an AC clunk noise, you have to open the panel and check all of these parts. Now, it’s actually really hard to look at an AC part like a compressor and diagnose if it’s malfunctioning. Even experienced HVAC repair guys use gauges, airflow meters, voltage meters, and so on to check if an AC part is working correctly.
More often than not, it’s best to call a professional HVAC repairman to check why your AC is making clunk noise.
Before you do that, however, try to:
- Check if you can see which part is generating the clunking noise.
- Decide if the clunking noise is something you feel bothered by.
Low clunking noise, especially in the outdoor AC unit, might not be that problematic. However, if you’re hearing a loud clunking noise, some part like a fan or compressor might be seriously damaged and can present a systemic danger to your whole AC unit. In that case, calling an expert is a smart idea.
Normal Noise Levels + Who You Should Call If You Have A Noisy AC Unit
The distinction between a noisy AC unit and a normally loud AC unit is important to understand. Every AC producer will specify the noise levels for each fan speed setting in the specifications. Based on that, we can see which are the quietest portable or window air conditioners.
However, when your AC is starting making high-pitched noises, that’s not a part of normal operation. If you can’t repair a noisy AC yourself, you should hire an HVAC repairman. You can get some quotes from certified HVAC repairmen here; they are specialized in diagnosing AC noises and fixing them.