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 determine the issue with your air conditioner. 

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

• The condenser fan motor on the unit may be unable to spin but still has power reaching it, creating resistance that results in 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 arrives at the level where cooling is necessary. When the contractor malfunctions, it can create 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 cannot trip, you might 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 several other possible causes such as a refrigerant leak, clogged air filter or faulty 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 close to the exterior condenser, you could 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 broken – like the blower motor failing, a broken condenser fan motor can also cause 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 sound as more of a hum than a buzz. There can be multiple causes for a failure of this part including debris rattling against the condenser, overgrowth surrounding the unit, loose parts, etc. 
• Loose components inside the air conditioner – Your HVAC system is an intricate machine with a lot of moving parts. Over time, it’s possible that a few 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 your 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 a sign that something inside your air conditioner is off and needs a closer look. Given the causes above, it’s beneficial to narrow down where the sound is coming from. Your whole HVAC system is interconnected. The air conditioner needs adequate airflow to operate correctly. Air passes 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 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 attempted by a homeowner, but only by a trained 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 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 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 & Plumbing, we will not only diagnose your problem and offer 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.