A/C Noises: What to Ignore and When to Call for Help

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A/C noises: are they simply an annoyance — or a warning of an impending cooling system breakdown this summer? Ideally, your central air conditioner keeps you comfortable while remaining well in the background of typical household sounds, barely registering in your awareness. Once you start noticing A/C noises, however, they may become hard to ignore. That’s the time to pay attention and decide what the sounds might mean and whether you need qualified service to deal with them. Here’s a rundown of typical A/C noises and what they signify:

  • Pops and booms from the vents. Normally, just temperature changes affecting the sheet metal used to fabricate the ductwork. The material warms and cools as the system cycles on and off, expanding and contracting slightly. Sheet metal makes sounds as it flexes, usually more noticeable at night when the house is quiet. Annoying, perhaps, but not indicative of any serious malfunction.
  • Noticeable whooshing or whistling noises. While some sounds of air in motion are normal, loud noises may indicate airflow imbalance inside the ductwork. Are A/C vents in some rooms closed? For proper balance, all vents in the house should be open. Also, ductwork leaks can expel air or draw excess air into the system, causing whooshing sounds and or whistling. A duct evaluation by a qualified HVAC technician can narrow down the causes.
  • Squeals and screeches. Particularly noticeable when the system initially cycles on, these are usually the result of a worn or slipping blower motor drive belt in the indoor air handler. Ask your contractor to check the belt tension and replace it if necessary.
  • Loud humming or clicking sound outdoors. Usually accompanied by failure to cool, this typically means a worn-out run capacitor that provides the necessary jolt of electricity to start the compressor and condenser fan installed in the outside half of the system. This component has a finite service life and is replaceable. Due to the high voltage hazard, it should only be done by a qualified HVAC service person.

For professional diagnosis and repair of A/C noises, contact Apollo Home Heating, Cooling, Electric and Plumbing.

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