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Common Noises Your AC Can Make and What They Mean


Has your AC recently started to make loud or unusual noises? Although you’ll always hear your AC running, excessive noise or unusual sounds are a sure sign that the system has a problem. In this article, we’ll look at some of the most common noises your AC can make, what each one means, and how they can be fixed.

Humming or Buzzing

Humming or buzzing sounds coming from the AC condenser outside your home isn’t something you should ever ignore. These sounds can indicate that the compressor motor or fan motor is starting to wear out. The first thing to check in this situation is if the fan at the top of the AC unit is running.

If the blower inside your home is running and you don’t see the fan blades spinning, you should immediately turn your AC off. You’ll then want to check and make sure that there are no sticks or other debris that are preventing the fan blades from spinning. If the fan is clear, it usually means that either the fan has a loose part or its motor is worn out and needs to be replaced. You never want to let your AC keep running if the fan isn’t working since this will usually cause the compressor motor to quickly start overheating and put it at risk of seizing up or burning out.

If you hear this type of noise and the unit isn’t running, it often means that the start capacitor is worn out. Both the compressor motor and condenser fan motor require a huge surge of electricity to start up. The start capacitor is similar to a large battery, and it releases its stored charge to help both of the motors start up smoothly. If the start capacitor is bad, the motors usually won’t be able to start and will produce a loud buzzing sound when they try to run.

Buzzing sounds can also be a sign of an electrical issue with the unit, such as a loose or damaged wire. You’ll also hear a buzzing sound if the contactor relay switch is broken. This switch is what receives the signal from the thermostat and sends the signal to the AC condenser. If the switch is broken, it will prevent your AC from running. Even if your AC seems to be working normally, we would always recommend shutting it off any time you hear a buzzing sound just to be safe. If the buzzing noise is due to an electrical issue, your AC could end up short-circuiting and suffering severe damage.


If you hear a hissing sound inside or outside your home when your AC is on, it almost always means that the system has a refrigerant leak in the evaporator coil, condenser coil, or copper refrigerant lines. This is also not something you should ignore, as a leak will quickly cause the refrigerant level to become too low for the system to keep working properly. If the refrigerant level is low, the refrigerant will start to get much colder and usually lead to the evaporator coil freezing up. This can be a major issue if you don’t realize that the system is frozen soon enough. If your AC continues running when the coil is frozen, the compressor motor could burn out and force you to replace your entire AC condenser unit.

Grinding, Squealing or Screeching

Grinding, squealing, or screeching sounds are usually related to either the blower or the condenser fan depending on whether the sound is coming from inside your home or outside. A metal-on-metal grinding sound typically indicates that either the blower or fan is loose and scraping against its housing. Sometimes one of the condenser fan blades can also get bent and start scraping.

Squealing or screeching noises are a fairly sure sign that the bearings that drive the blower motor or condenser fan motor are wearing out. In this case, you will want to get the bearings replaced as soon as possible. Replacing the bearings is a fairly simple job. However, if the bearings completely wear out, it can cause the motor to burn out and lead to a much more expensive air conditioning repair.


If you hear a clicking sound coming from the AC condenser when it tries to turn on, it almost always means that the start capacitor needs to be replaced. The blower motor also sometimes has its own start capacitor that will also repeatedly click if worn out. You’ll usually hear your thermostat click once when it signals your AC to run and again when it signals it to shut down. If your thermostat continually clicks, it means that the signal isn’t reaching the condenser due to a bad wire, broken contactor relay switch, or other electrical issue.

At Kane Heating And Air Conditioning, we have more than 20 years of experience helping customers in the Harker Heights, Hutto, and Round Rock areas with their air conditioning and heating needs. Our technicians offer expert HVAC repairs and maintenance, and we’re also ready to help if you need any heating or cooling installation services. For more information or to schedule an AC inspection, give us a call today.

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