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Noisy Split System AC: Are Dirty Air Filters To Blame?

by Feride Halma

Split system air conditioners have numerous advantages over ducted systems, especially when it comes to operating noise. Under normal conditions, the indoor blower unit(s) of your split system should run very quietly.

If one or more indoor units are making more noise than usual, it could be a sign of underlying problems. Dirty air filters are one of the most common causes of excessive operating noise in split AC systems. 

Why Do Dirty Air Filters Make Split Systems Noisy?

Each indoor blower unit attached to your split AC system is fitted with at least one air filter. These physical filters catch dust, hair, and other debris, and prevent them from entering the system. These filters are very important. If dust accumulates on the surface of the unit's heat exchanger, it can seriously affect the system's ability to generate cool air.

Over time, the filters will become clogged with collected dust and debris, which prevents air from flowing through the filter freely. If an air filter becomes too clogged, the unit's intake fan will work harder and spin faster as it tries to suck enough air through the filter. A fan motor working at full power to suck air through a clogged filter can generate a lot of noise, causing your indoor unit to make a loud humming or buzzing noise.

How Can I Clean My Split System's Air Filters?

The vast majority of split system models have air filters that are easy to remove and clean. Check the manufacturer's instruction manual that came with the system, which should contain instructions on how to locate, remove, and reinsert air filters. Make sure the split system is fully switched off before removing any filters.

Once removed, the air filters can be cleaned using a vacuum cleaner on low power. Lukewarm water will rinse away any impacted dirt. You can also purchase specialized filter cleaning detergents, which will clean the most badly clogged filters and may prolong the useful life of your filters.

What If Cleaning The Filters Doesn't Solve The Problem?

If you have thoroughly cleaned and properly reinserted the air filter(s), but your split system's indoor unit is still unusually noisy, you may be dealing with a more serious problem. The following mechanical problems can all cause excessive noise:

Burnt-Out Fan Motor

If the unit's fan motor has been running at full power for a long time to compensate for a clogged air filter, it may have been damaged by the constant overwork. It will need to be inspected by a professional AC repair service, and repaired or replaced as necessary.

Loose Fan Or Fan Housing

If the unit's blower fan, or the housing that contains it, has become loose, it may make a rattling noise while the unit is functioning. Call professional AC repair services to refit or replace the fan and/or fan housing.

Electrical Problems

If the unit's electrical wiring has been damaged by corrosion or recent remodeling work, the unit may make a loud buzzing noise. This problem will also have to be fixed by professional services and trying to repair electrical problems yourself can be both difficult and highly dangerous.

Contact a local AC repair service to learn more.