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

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

The condenser fan motor on the unit may be unable to spin but still has power reaching it, creating resistance that produces a pronounced—and often loud—humming noise.
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 required. When the contractor malfunctions, 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 faulty and won't, you might 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 malfunctioning 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 near the exterior condenser, you might 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 broken – similar to the blower motor failing, a broken condenser fan motor can also make 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 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 near 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 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 the refrigerant lines are undercharged, it can cause vibration. This vibration may 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 important to narrow down where the sound is coming from. Your whole HVAC system is one unit. The air conditioner requires adequate airflow to operate properly. 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 clogged, or the blower motor breaks, 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 completed 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 danger 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 life. The blower motor is not a part that needs to be replaced regularly. Working with Service Experts, we will not only diagnose your problem and offer recommendations to resolve things as soon as possible, we’ll also assess your HVAC system as a whole. 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.