Why is my air conditioner making a humming noise?

If your air conditioner is humming, it could 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 can include: 

  • The condenser fan motor on the unit could be unable to spin but still has power reaching it, creating resistance that results in a pronounced—and often loud—humming noise. 
  • There could be a mechanical or electrical failure with the contractor relay switch, the component responsible for starting the outside unit when the indoor temperature rises to the level where cooling is required. When the contractor fails, it can produce a humming sound. The switch is located 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 damaged and won’t, you might 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 a handful of other possible causes such as a refrigerant leak, clogged air filter or malfunctioning 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 close to the exterior condenser, you might mistake the source of the humming noise. With the AC running, found out 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 running 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 several causes for a failure of this part including debris entering the condenser, overgrowth near the unit, loose parts, etc. 
  • Loose components inside the air conditioner – Your HVAC system is a complex machine with a large number of moving parts. Over time, it’s possible that some parts broke loose due to typical wear and tear. A loose part can 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 a sign that something inside your air conditioner is off and needs attention. Given the causes above, it’s important to find where the sound is coming from. Your entire HVAC system is interconnected. The air conditioner needs adequate airflow to operate properly. Air passes 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 clogged, or the blower motor breaks, that can cause issues with your condenser unit located outside the home. 

Resolving 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 hiring 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 lifespan. The blower motor is not a part that needs to be replaced on a regular basis. Working with Service Experts Heating, Air Conditioning & Plumbing, we will not only diagnose your problem and provide recommendations to resolve things as soon as possible, we’ll also inspect your HVAC system as a whole. If your unit has 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. 

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