HVAC Troubleshooting: What is Causing My AC’s Loud Buzzing Noise?

Posted on: June 25, 2020

Why Is My AC Buzzing? Loud AC buzzing noise from an AC unit indicates stress on a HVAC system, specifically an electric issue.  It is important that you do not become familiar with the noise, and instead turn off your AC unit and call a licensed HVAC contractor. It is also important to distinguish the noise from rattling or grinding, as those sounds are a typically signs of malfunctioning parts, debris or misalignment.

Electrical

AC Buzzing noises are usually from electrical arcing – a discharge when electricity is jumping between circuitry. Loud buzzing noises indicate the electrical voltage flowing through your air conditioner is not at its correct amperage. Failing electrical components increases the risk of fire and should be diagnosed by a licensed HVAC expert to keep you and your home safe.

Motor

The motor needs to be lubricated with oil, especially in older AC units, to keep bearings from getting worn and eventually malfunctioning. A bent blade on the fan could also cause a buzzing noise. Lubricating the motor or replacing fan blades should be done before extensive use of AC (at the beginning of summer for example) to prevent a malfunctioning system later on.

Refrigerant

If a buzzing or hissing noise is coming from the AC unit itself, it could be a sign of a refrigerant leak. Refrigerant leaks cause AC units often freeze up, even during the hottest time of year when the AC is consistently on. Water dripping onto the motor will cause also an abnormal noise; the repair would involve locating the obstruction/leak and properly isolating the unit.

Parts

AC Buzzing Noises This is associated more with a rattling noise, but misalignment or loose screws/panels could also create a ‘buzzing’ noise. Poor installation or aged AC parts cause screws to become loose, also causing the panels on the cabinet to unfasten.

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