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 verify 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 leads to a pronounced—and often loud—humming sound. 
  • There could be a mechanical or electrical failure with the contractor relay switch, which is responsible for starting the outside unit when the indoor temperature reaches the level where cooling is needed. When the contractor breaks, 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 when it becomes overloaded. However, if the circuit breaker is malfunctioning and cannot trip, you might hear an electrical humming noise. 
  • Ice on condenser – if your unit freezes up, this can cause a loud humming or buzzing noise. If your air conditioner is frozen, there are a few other potential causes such as a refrigerant leak, clogged air filter or broken blower motor. A broken blower motor will sometimes create a humming or buzzing noise, and is located in your furnace. If the furnace is located near the exterior condenser, you may mistake the source of the humming noise. With the AC running, determine if the humming or buzzing is louder near the exterior condenser unit or the furnace. 
  • The AC Condenser Fan Motor is damaged – similar to the blower motor failing, a broken condenser fan motor can also create a humming noise when it malfunctions. If the indoor blower is running but the fan is not turning, your fan motor may emit a loud buzz. Some people perceive this sound 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 surrounding the unit, loose parts, etc. 
  • Loose components inside the air conditioner – Your HVAC system is a complex machine with plenty of moving parts. Over time, it’s possible that a handful of parts broke loose due to typical wear and tear. A loose part may cause premature wear and loud noises, including a humming noise. 
  • Refrigerant pipes are vibrating – If your 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, like an improperly mounted expansion valve. 

A humming sound is evidence that something inside your air conditioner is off and needs attention. Given the causes above, it’s crucial to narrow down where the sound is coming from. Your entire HVAC system is one unit. The air conditioner needs adequate airflow to operate effectively. Air blows through the air filter, and it’s the blower motor (located inside the furnace) that pushes 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. 

Resolving the AC humming issue does best with a technician to perform a diagnostic assessment on your whole unit. This work should never be completed by a homeowner, but only by a certified technician. 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 because of the risk 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 lifespan. The blower motor is not a component 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 share recommendations to resolve things as soon as possible, we’ll also inspect your HVAC system entirely. If your unit is better off 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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