Air Conditioner Buzzing When Off

Written By Lester Mclaughlin
Updated On

Are you wondering why your air conditioner is buzzing when off?

You’ve come to the right place!

In this Blue National HVAC guide, you’ll learn:

  • Why your AC unit buzzes when it is off
  • If the buzzing is expensive to fix
  • When to get help from an HVAC pro

And much more!

Air Conditioner Buzzing When Off

So, if you’re looking for answers as to why your air conditioner is buzzing when it’s off, keep reading our detailed guide below to get answers to all of your questions!

Why Is Your AC Unit Buzzing When It’s Off?

When an air conditioner buzzes when it’s not running, it is a sign of concern. Buzzing can mean there’s a severe issue with the AC unit which would necessitate a repair. However, it can also be a simple fix that any homeowner can do themselves.

Whenever you hear buzzing, squealing, or loud humming noises coming from your air conditioning unit, you should address them immediately. 

When air conditioners are many odd noises, that’s their way of telling you they need service. 

Here are the common causes of AC units buzzing:

Faulty Condenser Blower Motor

The condenser fan motor is located on the outside unit, or “condenser unit” of the central air conditioner. When the blower motor that drives the fan fails, the fan will either no longer spin or just barely turn. 

Debris, such as twigs, branches, and leaves, may fall into the condenser and block the fan. If that is the case, clearing the debris should fix the buzzing noise. 

Alternatively, the fan motor can have an electrical problem, loose fan blades, or the blower fan belt can be stretched or broken. In either case, these types of fan issues should be inspected and repaired by an HVAC professional

Electrical Problem

Many air conditioner electrical problems also generate buzzing noises when the AC system is off. Since electrical issues can further damage your AC unit by shorting out and is a potential fire hazard, we recommend that you cut power to your AC system by flipping the circuit breaker.

One of our trusted HVAC contractors can help diagnose and fix the problem for you- just give us a call. 

Here are the common electrical problems that cause buzzing: 

  • Bad contactor relay switch – A failing relay prevents power from getting to the condenser, or it can malfunction and cause the incorrect amount of energy or amps, which could make a buzzing noise
  • Loose wiring – damaged and loose wiring can short or cause a grounding fault, resulting in buzzing noises 
  • Failed capacitor – The capacitor brings the proper start-up charge to your condenser, and when it is failing, it can cause buzzing noises to occur
  • Faulty electrical connections – If the electrical connections between the various air conditioner components and circuit breaker are faulty, this could cause a buzz too 
  • Solenoid valve – Sometimes the solenoid valve will wear down, become loose, or lose good contact with the electrical wiring and cause buzzing

Vibrating Compressor

The compressor of your HVAC system moves the refrigerant through the refrigerant lines and the condenser and evaporator coils. It sits inside your condenser unit and has mechanical pieces that move and cause the compressor to vibrate.

To prevent vibration noises, the compressor sits on top of rubber isolation feet to absorb the vibration and minimize noise. If the isolation feet wear down enough, the compressor will vibrate against the concrete slab making a loud buzzing noise. 

Additionally, if there are any loose parts on the compressor, that can generate both a buzzing and a rattling noise too. Buzzing and humming sounds from vibrating compressors should be inspected and repaired by an HVAC contractor. 

Frozen Coils

Frozen evaporator coils can block airflow from your indoor blower and overwork the fan. Without adequate airflow, the AC unit won’t cool the home properly, and the air conditioner will stay on for far too long. This stresses the fan and other components, which could result in loud buzzing noises when it finally shuts off. 

Frozen coils can be caused by refrigerant leaks, dirty coils, a clogged air filter, and various other reasons. To determine what is causing the frozen coils and get them repaired, a certified HVAC technician will need to provide service.

Refrigerant Leak

If your air conditioner has a coolant leak, it may lose enough refrigerant to compromise its cooling capabilities. If the AC unit loses too much refrigerant, it will not be able to remove heat and will run for long periods and never cool the home. 

Running for extended periods and never reaching the setpoint on the thermostat puts stress on the compressor and blowers. If they are worked too hard, they can buzz or hum when the AC unit turns off. 

If your home is not cooling and you hear buzzing or hissing (a sign of a leak), you absolutely need to call an air conditioning repair specialist. 

Refrigerant leaks require EPA-certified HVAC technicians to perform inspection, repair and recharging as mandated by law. 

Clogged Air Filter

A dirty, clogged air filter has the same effect on your air conditioner’s airflow as iced-over evaporator coils- it can completely block it. By blocking the airflow, the AC unit’s components get overworked, stressed, and sometimes overheated, leading to the buzzing noise. 

Cleaning or replacing the dirty air filter is a quick, easy, and inexpensive solution to this buzz-generating issue. Homeowners can easily clean or replace their AC filters themselves or get the help of an HVAC pro.

Is A Buzzing Air Conditioner Dangerous?

A buzzing air conditioner can be dangerous since faulty electrical components or refrigerant leaks can cause it. Electrical issues can cause additional components to short and fail or, worse, start a fire. On the other hand, refrigerant gas can be harmful if it is inhaled in large quantities.

Due to the possibility of these noises being dangerous, all buzzing sounds from the air conditioner should be treated with caution and repair by an experienced HVAC contractor. Give us a call today if you need assistance! 

Is It Expensive To Fix A Buzzing Air Conditioner?

The average costs to fix a buzzing air conditioner depends on what is causing the noises in the first place. It can range from basically “free” (cleaning the filter) to hundreds of dollars. Here are the average costs for each type of repair: 

  • Fan blower motor: $240 to $700
  • Electrical issues: $100 to $300
  • Compressor: up to $2,000, however many air conditioners have extended compressor warranties
  • Frozen coils: $50 to $1,500 depending on the cause of the issue 
  • Refrigerant leak: $250 to $1,600 to repair the leak and $300 to $800 to recharge the refrigerant 

When To Call An HVAC Specialist

If your air conditioning system is buzzing when it is off, and you don’t know why, give our team of HVAC service experts a call for help. We’ll provide you with fantastic pricing, responsiveness, and customer service. If you want your repair done right and your air conditioner noise eliminated, then schedule service with our HVAC technicians. 

Meet Your HVAC Expert

Lester Mclaughlin

HVAC systems are highly technical and often is the most misunderstood part of the house. From ductwork to heat pumps, I've been exposed to all sorts of issues facing homeowners. It really irks me when a homeowner is given bad advice like refilling freon vs fixing a leak in the system. I'm here to help our website readers with their heating and a/c problems.
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