When your air conditioner is running, you should become accustomed to the common sounds that are created by the AC unit. However, after some time has passed, your AC unit may begin to make unexpected noises such as a humming or buzzing sound. This is a sound you should pay attention to because it can indicate electrical or mechanical problems with your AC. 

A Defective Condenser Fan Motor

There might be something wrong with the condenser fan motor, which may cause it to not spin properly. However, electricity is still traveling to the motor and this is creating resistance, which generates the humming sound. Also, the electricity flowing to the air conditioner might not be the right amperage. 

A Defective Contractor Relay Switch

Check the contractor relay switch. This device switches on high voltage to your outside compressor, but can sometimes wear out. The good news is that this part isn't expensive to replace. 

Worn Out Feet

The compressor sits on small rubber feet, which are designed to isolate the compressor. These feet can gradually become cracked and disintegrate. This can lead to your compressor not being balanced and may lead to the humming noise. 

A Frozen Unit

Your AC unit can potentially become frozen, even on the hottest days of summer. The frozen AC unit results from a leak in the refrigerant line. When this occurs, it can also generate a buzzing sound that can be heard in your unit.

Loose Parts

Another common cause of a buzzing sound is when parts are loose inside the AC unit. The act of these lose parts moving around inside can lead to the buzzing noise. Regardless, loose parts can preclude more serious problems developing for your AC unit.

Other Sounds to Listen For

Humming and buzzing are always bad sounds to hear, but there are several other sounds you should look out for, including:

• Rattling
• Clicking
• Clanging
• Screaming

Unusual sounds are almost always a sign that your AC unit needs to be serviced soon or you may be forced to replace the entire unit in the future. The last thing you want is for your AC unit to give out in the middle of summer.

When hearing a strange noise, the best thing you can do is turn off your AC immediately and contact an AC repair technician. If there is something wrong with your AC and you allow it to continue to run, you might be at risk of damaging the unit.