Central Air Condensing Unit Noisy? 4 Possible Causes

Home » Central Air Condensing Unit Noisy? 4 Possible Causes

You’re enjoying a peaceful summer afternoon on your back patio reading a good book or scrolling through barbeque recipes on your phone when you’re startled by the central air condensing unit turning on. The calming sounds of the birds and insects are now obliterated by loud rattling, buzzing, or squealing sounds coming out of the a/c condenser, disrupting the peace, and sending you running back into the house where the noise level is more tolerable.

Does keeping your home at a comfortable temperature during the hottest days of the year need to be so loud? We at Repair Clinic.com know it doesn’t! There are four likely causes for why your central a/c condenser unit has gotten very noisy during operation. Before we begin troubleshooting, let’s review how the condensing unit works.

What is a central a/c condenser unit and how does it work?

What is a central a/c condenser unit? It is one of two units required to lower the air temperature in your home (the other unit is your furnace, or air handler, which can be located in the basement, attic, or a closet space within the house or apartment). The central a/c condensing unit is normally mounted on a slab of concrete directly behind the home or at the side of the house. The unit has a series of condenser coils around the outside of the unit with a fan motor and fan blades mounted to a grille on top. Other components found in the a/c condenser include a compressor, a filter-drier, a contactor, and a capacitor.

The condensing unit and furnace (or air handler) work together to cool your home

A wall thermostat regulates the temperature in the home. When the thermostat is lowered or it detects an increase in temperature, it closes a cooling circuit, allowing voltage to travel to a control board. The control board will then send 120 volts of alternating current to a circulation blower fan in the furnace or air handler and 24 volts to the contactor in the outside condensing unit. When the contactor is energized, it allows 240 volts to flow through a nearby disconnect box to the compressor and condenser fan motor located in the condensing unit.

Single vs. dual run capacitor

The capacitor, which stores an electrical charge, then releases it, may be a single run capacitor or a dual run capacitor. A single-run capacitor will power just the compressor or the condenser fan motor. Still, the majority of a/c condensing units will use a dual-run capacitor that can power both the compressor and the fan motor.

How the a/c condenser compressor and fan motor work

The compressor acts as a pump, compressing refrigerant in gas form into the condensing unit’s condenser coils. A filter-drier is often attached to the refrigerant line to remove moisture from the refrigerant. Once the refrigerant gas enters the condenser coils, it is condensed into a hot liquid. The condenser coils dissipate the heat as the liquid travels through them, assisted by the spinning condenser fan motor blades. After passing through the condenser coils, the refrigerant travels to the evaporator coils mounted on the furnace or air handler. There the refrigerant expands back into a gas which makes the coils cold. The circulation blower fan draws air past the cold evaporator coils and forces the air through the venting to cool the interior of the home.

4 reasons your central a/c condenser is noisy

If the condenser unit outside the home is making a racket every time the central air conditioning system initiates operation, Repair Clinic has four potential causes you should investigate so you can restore the peace and quiet:

  1. Annoying buzzing – Are you hearing a buzzing sound when the a/c condenser unit is running? The condensing fan motor blade may be damaged or loose. If the blade wiggles on the motor shaft, you should first try to tighten the set screw securing the blade to the shaft. If the screw simply won’t tighten properly, you should be able to replace the screw with a new one. If the condensing fan blade is visibly bent or damaged, the blade itself should be replaced.
  2. Unsettling screeching or shrieking – The condenser fan motor has bearings that wear out over time and can cause the motor to make a buzzing sound if the bearings are just beginning to fail and a louder screeching or shrieking sound if they are getting ready to fail completely. Try rotating the condensing fan blade by hand. Does it turn freely or is it difficult to turn? Do you hear a rattling or grinding sound when rotating the fan blade? If the blade is difficult to turn or produces a noise when being turned, that’s a strong indication that the motor bearings are worn out. Since the bearings cannot be repaired, you will need to install a new condenser fan motor to solve the noise problem. Be aware, that if you’re hearing a buzzing or screeching sound coming from the furnace, it’s likely the circulation blower fan motor bearings are failing.
  3. Loud chattering or humming – An a/c condenser contactor that is faulty may make a chattering or humming sound. If the contactor contacts show signs of wear or burn marks, or you’ve determined the component is the source of the noise, the contactor should be replaced.
  4. Worrisome banging and clanging – The compressor, which pumps the refrigerant through the central air condensing unit coils, can become loud or noisy as it ages. After years of use, it’s not uncommon for the components inside the compressor to loosen or detach, creating a banging or clanging sound when the compressor is running. While some compressors can continue to work efficiently for years after they become noisy, Repair Clinic recommends having a licensed professional install a new compressor, not just to reduce the noise level, but to ensure the a/c condenser unit will run optimally.

Learn how to fix your central air condensing unit with Repair Clinic

How can you easily replace a central air condensing unit fan motor, fan blade, or contactor? By exploring Repair Clinic’s “Videos & Articles” library, a free resource filled with thousands of troubleshooting and step-by-step procedural videos, articles, diagrams, and schematics designed to guide do-it-yourselfers and professional technicians alike with fixing heating and cooling systems, outdoor power equipment, and all major home appliances. Enter the full model number of the condenser unit in the website’s search bar to locate the specific help you need. Are you a handyman? We have an array of how-to videos just for you to assist in fixing the fan motor, fan blade, and contactor on a Goodman (Model GSX130481BG) central air condensing unit, a Lennox (Model 13ACXN03623017) condensing unit, and many more!

Repair Clinic stocks genuine OEM central air condensing unit parts

Regardless of which central air condensing unit component you need to replace, you’ll want to make sure you’re purchasing a genuine manufacturer part and not just a cheaply-made knock-off. As your repair partner, Repair Clinic stocks genuine OEM central air condensing unit parts from such major heating and cooling brands as Lennox, Frigidaire, Goodman, Rheem, York, Carrier, Payne, and Honeywell. You can find the exact central a/c condensing unit part that works with your central a/c unit. Partner up with Repair Clinic and you’ll save time and money on every repair.

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