How to Remove Musty Smells from Central Air Conditioning


Suzanne asked: I have one room that was an addition to my house. Previous owner had the garage made into a room. The air conditioning smells so must. It comes out of two vents in the ceiling. I have had the unit serviced and keep the filter clean. The unit is in a small attic off the master bedroom. Any ideas? Thanks

If a musty odor is coming from the air conditioning, it means that there is mold, mildew, slime or other growth somewhere in the unit. There are two key places to check when trying to locate the source of the problem. The first is the unit itself, which is located outside. The second is the air handler which is located in the house somewhere. The air handler is typically located in the attic or basement and contains the air filter that is changed frequently.

Once the air handler is located, check to ensure that the water is draining properly from the condensate drain. A good time to check this is after the air conditioner is turned off on a humid day. If there is mold or growth present, it may help to add a small amount of bleach to the drain pan and drain line. There are special cleaning sprays available to clean the evaporator coils. Once the growth is removed, the smell of the air should freshen.


  1. Indiana Person says:

    Get a can of Lysol Spray and while the blower is on sucking air through the system, spray Lysol at the intake so it will suck the mist all the way through your system. Also, spray down all the coils and areas that water can stand inside your central air system.

  2. Peter says:

    Whoever wrote this does not seem to understand that the outdoor equipment called a condensing unit (shown in the picture) does not bring any air into or out of the home. Only the cooling liquid is circulated through it; the fan helps cool the liquid.

  3. Ruth says:

    We have a mini-split system, I cleaned the filter with hot soapy water a few days ago, and yesterday it started to smell very musty. What do you suggest I do to get rid of this smell? I can’t stand it!!

  4. Melanie says:

    Since the smell only started after you washed the filter, I would suggest re-washing the filter. This time, make sure that the filter is completely dry before putting it back in the AC unit. This article may help: How to Clean Your Home’s Air Filter.
    Allowing the filter to dry in direct sunlight could also help to kill any bacteria or odor on the filter.
    If needed, you can always replace the filter instead.

  5. Irma says:

    My AC unit is new, but every time it kicks on, it smells like I had a house full of cat pee. Please help. Thank you.

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