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 verify the issue with your air conditioner. 

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

• The condenser fan motor on the unit may be unable to spin but is still connected to power, 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 rises to the level where cooling is necessary. When the contractor malfunctions, 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 damaged and won’t, you can hear an electrical humming noise. 
• Ice on condenser – if your unit freezes up, this can result in 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 installed close to the exterior condenser, you may mistake the source of the humming noise. With the AC running, check to see if the humming or buzzing is louder near the exterior condenser unit or the furnace. 
• The AC Condenser Fan Motor is broken – similar to the blower motor failing, a broken condenser fan motor can also cause 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 noise as more of a hum than a buzz. There can be different causes for a failure of this component including debris entering the condenser, overgrowth around 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 a handful of 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 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, such as an improperly mounted expansion valve. 

A humming sound is a sign that something inside your air conditioner is off and needs a closer look. Given the causes above, it’s helpful to find where the sound is coming from. Your entire HVAC system is interconnected. The air conditioner requires adequate airflow to operate correctly. 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 clogged, or the blower motor malfunctions, that can cause issues with your condenser unit located outside the home. 

Resolving 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 technician. 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 due to 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 often. Working with Service Experts Heating & Air Conditioning, we will not only diagnose your problem and provide recommendations to resolve things as soon as possible, we’ll also review your HVAC system as a whole. If your unit needs 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.