Why is my air conditioner making a humming noise?

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

Potential causes of your cooling system’s humming might include: 

  • The condenser fan motor on the unit might be unable to spin but is still connected to power, creating resistance that leads to a pronounced—and often loud—humming sound. 
  • There could be a mechanical or electrical malfunction with the contractor relay switch, which is responsible for starting the outside unit when the indoor temperature reaches the level where cooling is necessary. When the contractor fails, it can create a humming sound. The switch should be 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 broken and can’t, you may hear an electrical humming noise. 
  • Ice on condenser – if your unit freezes over, this can cause a loud humming or buzzing noise. If your air conditioner is frozen, there are a handful of other potential causes such as a refrigerant leak, clogged air filter or broken blower motor. A broken blower motor will often create a humming or buzzing noise, and is located in your furnace. If the furnace is located 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 working 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 reaching the condenser, overgrowth near the unit, loose parts, etc. 
  • Loose components inside the air conditioner – Your HVAC system is a complex machine with a lot of moving parts. Over time, it’s possible that some parts came loose due to normal 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 can 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 find where the sound is coming from. Your entire HVAC system is interconnected. The air conditioner relies on adequate airflow to operate correctly. Air blows through the air filter, and it’s the blower motor (located inside the furnace) that circulates air through the entire system to heat or cool your home. If the air filter is dirty, or the blower motor breaks, that can cause issues with your condenser unit located outside the home. 

Fixing the AC humming issue requires a technician to perform a diagnostic assessment on your whole unit. This work should never be completed by a homeowner, but only by a trained 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 due to the risk of electrocution. Homeowners are better served hiring an HVAC company to diagnose 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 damaged, 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 on a regular basis. Working with Stevenson Service Experts, we will not only diagnose your problem and provide recommendations to resolve things as soon as possible, we’ll also assess 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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