Why is my air conditioner making a humming noise?

If your air conditioner is humming, it might mean there is an electrical or mechanical problem. Take steps now to determine the issue with your air conditioner. 

Possible causes of your cooling system’s humming may include: 

• The condenser fan motor on the unit could be unable to spin but is still connected to power, creating resistance that results in a pronounced—and often loud—humming noise. 
• There could be a mechanical or electrical breakdown with the contractor relay switch, which is responsible for starting the outside unit when the indoor temperature rises to the level where cooling is needed. When the contractor breaks, it can create a humming sound. The switch can be found in the exterior condenser unit outside your home. 
• The circuit breaker is overloaded – normally, your circuit breaker trips if it becomes overloaded. However, if the circuit breaker is faulty and cannot trip, you may hear an electrical humming noise. 
• Ice on condenser – if your unit freezes over, this can result in a loud humming or buzzing noise. If your air conditioner is frozen, there are several other possible causes such as a refrigerant leak, clogged air filter or damaged blower motor. A broken blower motor will sometimes create a humming or buzzing noise, and is located in your furnace. If the furnace is positioned near the exterior condenser, you could mistake the source of the humming noise. With the AC running, check to see if the humming or buzzing is louder near the exterior condenser unit or the furnace. 
• The AC Condenser Fan Motor is damaged – like the blower motor failing, a broken condenser fan motor can also create a humming noise when it fails. If the indoor blower is on but the fan is not turning, your fan motor may emit a loud buzz. Some people perceive this noise as more of a hum than a buzz. There can be different causes for a failure of this part including debris reaching the condenser, overgrowth around the unit, loose parts, etc. 
• Loose components inside the air conditioner – Your HVAC system is an intricate machine with a lot of moving parts. Over time, it’s possible that some parts shook loose due to normal wear and tear. A loose part may cause premature wear and loud noises, including a humming noise. 
• Refrigerant pipes are vibrating – If the refrigerant lines are undercharged, it can cause vibration. This vibration may sometimes sound like a humming noise. There may be other causes for a vibrating refrigerant line, such as an improperly mounted expansion valve. 

A humming sound is evidence that something inside your air conditioner is off and needs a closer look. Given the causes above, it’s beneficial to determine where the sound is coming from. Your entire HVAC system is interconnected. The air conditioner needs adequate airflow to operate correctly. Air blows through the air filter, and it’s the blower motor (located inside the furnace) that moves air through the entire system to heat or cool your home. If the air filter is dirty, or the blower motor malfunctions, that can cause issues with your condenser unit located outside the home. 

Fixing the AC humming issue does best with a technician to perform a diagnostic assessment on your whole unit. This work should never be attempted by a homeowner, but only by a trained professional. Your HVAC system has hazardous refrigerants running through it that should be safely handled only by a professional. Electrical components to your system should never be adjusted by a novice due to the danger of electrocution. Homeowners are better served calling an HVAC company to examine and repair their system if they notice any odd humming, whirring, or buzzing noises coming from their unit.  

If a component like the blower motor is faulty, it may be because your furnace is near the end of its life. The blower motor is not a component that needs to be replaced regularly. Working with Service Experts Heating & Air Conditioning, we will not only diagnose your problem and offer recommendations to resolve things as soon as possible, we’ll also review your HVAC system as a whole. If your unit needs to be replaced, we have affordable options with top tier service available through financing. We also have the Advantage program that will get you a new system for a low monthly rate.