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 identify the issue with your air conditioner. 

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

• The condenser fan motor on the unit may 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, the component responsible for starting the outside unit when the indoor temperature reaches the level where cooling is required. When the contractor malfunctions, 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 when it becomes overloaded. However, if the circuit breaker is broken 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 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 close to the exterior condenser, you could 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 – like the blower motor failing, a broken condenser fan motor can also make a humming noise when it malfunctions. If the indoor blower is working 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 component including debris rattling against the condenser, overgrowth near the unit, loose parts, etc. 
• Loose components inside the air conditioner – Your HVAC system is an intricate 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 will 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 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. 

Resolving the AC humming issue does best with 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 trusting 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 often. Working with Robinson Service Experts, 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.