Please help...mildew smell from central AC

cheri127July 30, 2007

Forgive me if I'm asking a repeat question. I tried doing a search and couldn't find anything directly related to my problem.

I bought a beach house last year (new construction, but almost 2 yrs old) and by the end of the summer, the central AC started to have a mildewy smell. We have two units, one for the first floor and one for the second and it's only the first floor that smells bad and it only smells with the AC not with the heat. You can smell it from all of the vents but it's worse in the powder room and at the return vent, which are near each other. The air handler is in the utility room on the first floor but the duct work runs through the crawl space under the house.

Coincidentally, the compressor on this unit just went bad. Even with the AC off, I still have the smell coming from the powder room and return vent. I'm waiting for the new compressor to come in and would like to discuss the smell problem with the technician when he comes to do the install. Does anyone have any idea what could be causing this odor and what I can do about it? My daughter is allergic to mold and I'm hypersensitive to odors so this is a real problem for us.

Any advice/information would really be appreciated. Thanks.


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The condensate (water) probably isn't draining properly, and mildew is growing in the pool of water or the damp parts. That should be fixable, because it's not something that should happen.

    Bookmark   July 30, 2007 at 2:02PM
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So, is the condensate collecting in the ducts? The technician is coming Thursday to install the new compressor. I'd like to go over all possiblities for the cause of this smell with him so I can get it fixed. Any other causes that anyone knows of?

    Bookmark   July 31, 2007 at 10:29AM
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The condensate water is usually in the pan under the air conditioning coil in the air handler inside the house. There should be a condensate drain line running from the air handler to a location where the water drains. Do you see water on the floor by the air handler? Is your filter wet? Can you see or hear condensate water flowing from the line? You can put a little bleach inside the pan or the drain line to kill the mold/mildew.

    Bookmark   July 31, 2007 at 12:12PM
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I copied this from another forum:

"This isn't as bad as you might think. Dirtys sock syndrome is bacteria growing, usuallly in the coil and pan area. The solution is for your service company to do a thorough cleaning of the indoor coil, pan and drain, using a good, stiff mix of coil cleaner and disinfectant, like Lysol. The entire area must be kept WET for at least 10-minutes and then be thoroughly rinsed to flush away the bacteria."

    Bookmark   July 31, 2007 at 1:07PM
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Thanks for the info, Gary. I just cleaned the filter and it wasn't wet, but I didn't check the line or pan. I'll have the technician do a thorough inspection of the air handler and maybe even the duct work, particularly the ducts where the smell is strongest.

    Bookmark   July 31, 2007 at 10:54PM
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