Why is my AC making noises!

Why is my AC making noises!

Summer is around the corner. This means hot days are approaching and your AC will be needed to keep you comfortable in your home.

In addition to routine maintenance, check for any unusual or unexpected noises coming from your AC unit. These noises signal trouble with your unit and may require immediate attention. Here’s a guide to these noises and actions you can take:

Squealing From Blower Motor

Your AC unit’s motor may have a bad belt or bearing. You can replace the belt yourself if you choose since it is an inexpensive and easy task. This should be done as soon as possible since a bad belt can lead to a broken belt which will prevent the blower from turning. Also, if your motor unit has oil ports, you may want to change or fill the ports with motor oil to help soften motor noises. Always research appropriate oil before using as each motor will have its own specification.

Loud Rattling or Banging

These sounds typically originate from either loose fasteners on the metal cage or a component of the blower assembly or motor which has come loose. Loose fasteners require tightening screws or bolts that secure the cage. A more complicated problem will be if the problem is with a component on the blower assembly. If not addressed, this rattling will get louder and may result in the disconnection of the blower itself. As this is a more complicated issue, you may want to do more research before attempting to address the issue yourself. Or you may want to call a certified HVAC technician to fix the issue.


Normally, your unit will click as it is being turned on and off but if the clicking is abnormally loud and coming from inside the cabinet, your capacitor may be on the way out and should be replaced. As a short term battery supply for the compressor and blower motor, the capacitor is a critical part of your AC unit and can wear down over time. An ineffective capacitor can put stress on the compressor which can in turn affect the overall health of your entire HVAC system. If you think your capacitor is making the clicking sound, turn off your AC unit immediately and contact a certified HVAC technician to replace the part.


If your AC unit does not turn on and your clicking sound has turned into a hum, this can be a very serious problem indicating the compressor is being used as a power source and can quickly lead to costly repairs. For this reason, we suggest that you turn off your AC unit to prevent further damage. These parts also have a tendency to fail during the warmest part of summer when your AC unit is working harder than normal. To avoid a breakdown, make sure to have a certified HVAC technician address this problem as soon as it is detected.

Loud Whistles or Screaming Noises

These types of noises are critical and can be very dangerous as they may indicate a refrigerant leak or internal pressure buildup. This needs immediate attention by a certified HVAC technician. If there is a 24-hour hotline for your specific technician, it is best to use that route as they may be able to diagnose the issue over the phone and provide next steps.

Metal on Metal

If this noise is coming from the fan, your blades may be the culprit. It is possible a foreign object like loose wiring or stones may be in contact with the blade. If not addressed, the blades may be damaged as well as the motor. This can even lead to a refrigerant leak. If you hear this type of sound, turn off your unit immediately and investigate what may be obstructing the blade(s). If the culprit can be removed manually, then cleaning and clearing the debris will fix the issue. A routine visual inspection of the fan and blades should be performed frequently while your unit is being used.

In summary, proactive and routine maintenance can help to prevent your AC unit from breaking down unexpectedly.

If your AC is making any of these strange sounds and you live between Burlingame and Sunnyvale, give Sal a call at (650) 575-3915.