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 identify the issue with your air conditioner. 

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

  • The condenser fan motor on the unit could be unable to spin but still has power reaching it, creating resistance that produces a pronounced—and often loud—humming sound. 
  • 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 reaches the level where cooling is necessary. When the contractor breaks, it can produce 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 damaged and can’t, you might hear an electrical humming noise. 
  • Ice on condenser – if your unit freezes over, this can produce a loud humming or buzzing noise. If your air conditioner is frozen, there are a few other possible causes such as a refrigerant leak, clogged air filter or malfunctioning 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 near the exterior condenser, you may 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 – similar to 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 sound as more of a hum than a buzz. There can be multiple causes for a failure of this part including debris reaching 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 some parts broke 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 your 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, such as 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 helpful to narrow down where the sound is coming from. Your whole HVAC system is interconnected. The air conditioner requires adequate airflow to operate normally. Air passes 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 the whole unit. This work should never be attempted by a homeowner, but only by a certified professional. Your HVAC system has hazardous refrigerants running through it that should be carefully 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 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 lifespan. 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 share recommendations to resolve things as soon as possible, we’ll also assess 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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