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Common AC Noises and What They Mean

an air conditioning vent

Learning about normal AC noise versus AC noise that signals a problem is important. This knowledge comes in handy for anyone wanting to know what to do if their AC breaks. After all, there are several noises AC systems commonly make that are perfectly normal. Knowing what isn’t normal is key to keeping your AC in good working order and extending its life as long as possible.

There are a few normal sounds that any well-running AC might make. There’s the humming, starting-up sound the AC makes when it first kicks on, for example. There’s also the gentle whirring noise the outdoor condenser unit makes while it runs. The metal ductwork that connects your AC to the vents in your home might also make noises over time. These sounds come from normal expansion and contraction due to temperature changes through the seasons.

Other noises, on the other hand, can mean the AC has a broken part or is about to fail. One rule of thumb is that if your AC starts making a new, unusual sound, there’s a good chance something is going wrong. If you know the sounds that an AC might make when it’s having a problem, you can figure out what’s going wrong and how to address it.

AC Screeching or Squealing Noise

If your AC starts making a loud, high-pitched screeching or squealing sound, it could mean the fan belt within the unit is loose and needs to be replaced. This isn’t a hugely complicated problem or repair. Experienced DIY homeowners might be able to tackle this themselves. Most people, however, will want to call in an experienced professional to handle it. Keep in mind that replacing parts on your AC unit can expose you to the risk of electric shock. Even smaller jobs are often best handled by a pro.

Screeching sounds that happen only when the AC first comes on can mean dangerously high pressure is building up within the compressor unit. If this is happening with your AC, turn it off as soon as possible. Then, contact a heating and cooling professional who can determine what needs to be done. This is not a good DIY project since it involves a high level of danger from the high pressure.

AC Rattling Noise

If your AC is making a rattling noise, it could be something as simple as dead leaves that have fallen into the outdoor unit and are blowing around inside. If you decide to open the condenser unit to clean it out, be sure to shut off the power to the unit first. The risk of electric shock is always present when working with AC units, so the power should be off at the breaker.

A rattling noise could also be due to other loose items within the unit. It may be a loose screw, panel or fan blade. Rattling sounds can also come from more complicated issues. Therefore, it may be best to contact a specialist to inspect the unit and determine the source of the noise.

AC Banging or Clanking Noise

A banging or clanking noise coming from your AC typically means there is a loose or unbalanced part somewhere within the system. The compressor unit has internal moving parts that can come loose. There are connecting rods and crankshafts that may wear out over time. The blower assembly may also be loose or unbalanced.

Whatever the cause, a sudden banging or clanking noise coming from your AC should be diagnosed by a heating and cooling specialist. It may mean the blower or some other internal part needs to be repaired. But it could also mean the AC unit is breaking.

AC Hissing or Whistling Noise

Your whole-house AC system includes many feet of ductwork that connect from the AC to the vents in each room of your home. They are the ducts that carry heated or cooled air throughout your home to keep it comfortable. Sometimes, this ductwork can develop cracks or holes. This happens over time, with age. It can also happen if rodents gnaw on the ductwork.

Either way, holes in the ductwork can cause a hissing or whistling sound that happens anytime the AC is on and air is blowing through the vents. If your AC is making this type of noise, you might also notice that air isn’t blowing as strongly out of the vents as it should be. This is another symptom of holes somewhere in the ductwork. A professional will be able to inspect all the ductwork in your home and find any holes in need of repair.

Hissing or whistling noises can also occur due to other issues. If you don’t have the right size or type of air filters, for example, air will whistle around the edges, causing strange noises. An expansion valve that isn’t compatible with your AC system could also cause hissing or whistling sounds. If you have an ongoing sound like this and you aren’t sure of the cause, it’s time to call in a pro to investigate.

AC Buzzing or Humming Noise

Most AC units make a quiet humming sound while they run. They might also make a more noticeable humming sound when the system first kicks on for a new cycle. These humming sounds are normal and not something to worry about. But when the humming sound is new or suddenly louder than usual, that’s cause for concern.

The same is true if the sound is more of a buzzing than a humming. A buzzing sound could mean there are loose screws or other parts somewhere within the system that need to be tightened up or replaced. Loose fan blades, or a loose or failing fan motor, can also make a buzzing sound in the outdoor condenser unit.

Another possibility for loud humming or buzzing noises coming from your AC is dirty parts that need cleaning. Dirty coils on the condenser can cause this type of noise. Debris in the indoor or outdoor units can also cause these sounds.

Buzzing sounds can also be caused by problems with the AC’s electrical wiring. This type of problem is dangerous to diagnose and fix, due to the risk of electric shock. If your AC starts to make a weird buzzing sound, the best thing to do is to shut it off and contact a professional to figure out what’s wrong.

AC Clicking Noise

Many AC units make one clicking sound when they turn on at the start of a new cycle, and another when they shut off at the end of the cycle. This gentle clicking noise is normal. If your AC starts making a more frequent or constant clicking sound, on the other hand, it’s time to get it checked out by a professional.

The noise may be caused by a malfunctioning thermostat or a defective contactor within the unit. These are typically not repairs that DIY homeowners can handle on their own. They are both more complicated AC repairs that are best handled by a pro.

AC Gurgling or Bubbling Noise

Bubbling or gurgling sounds coming from the AC are often caused by a blocked or cracked drainage pipe. The crack or clog in the line is causing a buildup of moisture and can also lead to dirty sock syndrome. Handy DIY homeowners can take a look at the drainage pan under the AC unit and also at the drain pipe, to see if there is a water or blockage situation happening. If you decide to tackle this issue yourself, be sure to turn off the power to your AC first.

Keep in mind, though, gurgling or bubbling noises can also be caused by refrigerant leaks. If there’s a leak of this type in your AC system, it’s a serious issue that should be handled as soon as possible by a professional.

AC Pulsating Noise

A minor pulsating noise that’s coming from the outdoor AC unit could be normal. There are moving parts within the condenser unit that do make this type of sound when functioning perfectly normally. But if you hear a loud pulsating sound coming from the AC, especially if it’s loud enough to hear from inside, it’s time to call in a pro. This noise could mean there is a loose or unbalanced part within the AC unit.

Any issue your AC may be having can be quickly diagnosed and fixed by a heating and cooling professional. Hiring a pro to conduct regular maintenance checks on your AC system is another smart way to keep it functioning efficiently and extend its life as long as possible. A pro can spot problems early on during routine air conditioning preventative maintenance. This will prevent small issues from damaging other components in the system and turning into bigger, more expensive AC repairs.

ABC Can Diagnose and Fix AC Problems

It can be quite alarming when you hear strange noises coming from your air conditioning unit. If you’re concerned about your AC unit, contact ABC Home & Commercial Services. Our licensed professionals can provide any needed AC repair and are available all day and all night.

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