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Some air conditioners are loud. Some are quiet. After you’ve lived with an AC unit for a while, you know the normal noise that it makes. If your air conditioner begins making a strange or louder than usual noise, it’s a sign that there may be something wrong with your system. Of course, if your air conditioner begins making a strange noise, generally the safest course is to shut it off and call your trusted, licensed HVAC service provider. That said, here are a few of the weird noises your air conditioner might make as well as what they may mean.

Screaming or Whistling

If your air conditioner begins to scream or whistle like a tea kettle, turn it off immediately! And call your trusted, licensed HVAC service company right away. These high-pitched noises can be from a serious refrigerant leak. Refrigerant gas can contaminate your home’s air, potentially making your family sick.

On the other hand, screaming could be a sign that too much pressure has built up inside of the compressor. Again, this is a potentially dangerous situation. Turn off your air conditioner and don’t turn it back on again until you have it inspected by a licensed HVAC technician.

Squealing

Some air conditioners squeal whenever they start up—it’s annoying but normal. However, if your air conditioner suddenly starts squealing, that’s a sign of a problem.

  1. Squealing could mean that either the outdoor fan motor or the indoor blower motor is going bad.
  2. In an older unit squealing could just be a sign of a belt that has slipped or needs to be replaced (newer units don’t usually use belts).
  3. Squealing can also simply be a sign of needing lubrication.

Whatever the underlying cause, squealing indicates that the unit needs to be serviced before more damage is done or it breaks down completely.

Banging or Clanking

If you hear banging or clanking from your air conditioner, you should shut it off immediately. These noises are often a sign that some part inside of the AC has broken loose or that the compressor has failed. If that loose part continues banging around, it could do more damage inside of the unit. Another cause of banging and clanking noises is a blower or fan that has gotten out of balance and is striking against other parts inside the unit as it turns. Again, this needs to be stopped immediately to avoid causing further damage. Shut it off from the thermostat and call your trusted, licensed HVAC service provider.

Constant Clicking

It’s normal to hear clicking noises when the AC is starting and stopping, but if the clicking continues throughout the run cycle, then you may have a problem. Constant clicking is generally a sign of a problem with the electrical components inside of your air conditioner, although it can also be due to a faulty thermostat. Either way, it’s definitely something you’ll want to get a licensed HVAC technician to check out.

Buzzing

A buzzing noise coming from your air conditioner can have quite a few different causes.

  1. Buzzing can be caused by an electrical issue. In that case, the buzz is the sound of electricity arcing. This could be caused by a circuit breaker or contactor relay switch going bad, or by a bad connection between any of the electrical components.
  2. Buzzing can also be caused by other issues. It could be something as simple as debris, like dead leaves, getting inside of the unit. Or the copper lines that carry refrigerant from the inside unit to the outside unit and back may be rubbing against something.
  3. Dirty coils or a dirty air filter can lead to a loud humming or buzzing noise as well, as your unit struggles with decreased air flow. Parts that are loose or out of balance—but not quite badly enough yet to “clank”—might also cause a buzzing sound.
    If your unit is buzzing, you might want to try checking the air filter and replacing it if it’s dirty to see if that alleviates the noise. But if the filter is clean and the unit is still buzzing, then it’s time to call for service

Rattling

The good news is that if your AC unit starts rattling, it’s probably NOT because a snake got inside! (Although we can’t guarantee it isn’t—you wouldn’t believe the critters we’ve found inside of HVAC systems over the years!) Rattling noises can be caused by a few different issues that have nothing to do with reptiles.

Air conditioners vibrate when they run, and over the years, this can cause the screws holding the system together to come loose. Then when the unit runs and vibrates, those screws and the parts that aren’t tightly held together anymore can make a rattling noise. This is generally a simple problem to fix—the screws just need to be tightened.

A rattling or clacking noise—like cards in the spokes of a bicycle—can also be caused by debris getting into the unit. For instance, if a twig has gotten into your outdoor unit and the fan hits it every time it turns, it can make a racket. If this is allowed to continue, it can cause damage to your fan’s motor over time.

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