[aag1974]

Was changing the filter today, and noticed something that looks like mold on it (see the attached picture).
- The filter is ~2 months old
- The unit (upstairs) is ~15 months old
- The downstairs unit (over 14 years old) doesn't seem to be affected

How concerned should I be?

 

[rcstl]

If that filter was dry when you removed it, you may be seeing mold where none exists. Mold likes to cuddle in warm places with moisture.

 

[aag1974]

It was indeed dry. I'm running a basic test on it (e.g. pour some bleach and see if the black disappears). After 5 min, it looks like this ... will check again tomorrow.

 

[rcstl]

A better test would be bleach in a bucket, filter suspended above and bucket covered. If the black goes away from bleach fumes, you gotta problem. If it remains, it is airborne junk.

 

[edgarbrown]

UV air purification might help.

Edgar
www.consumerscomfort.com

 

[teddy bear]

The mold test described are questionable. Look at under a microscope to verify mold growth. Looks like mold but not sure. Look behind the filter and around the cooling coil for more proof. Operating the blower a couple hours a day to avoid constant high moisture helps also.
If the filter looks like picture after a cooling season, not much of a problem.
Also keeping the home <55%RH during the cooling season also helps drying out the a/c ducts during off peak load everyday.
Keep us posted about a thorough inspection with a bright light. Many molds generate a slight odors.
For an interesting project, put a piece of the wet filter in a zip lock bag for a week, inspecting each day. This will demonstrates mold growth. Scary.
Regards Teddy Bear

 

[aag1974]

Thanks guys! HVAC tech was out yesterday, and gave the system a through check. There's no signs of mold anywhere else (coil, return box, etc). The best explanation he could find was that the filter door wasn't hermetically closed (which coincidentally it wasn't the day he was here, after I replaced the filter a day earlier) resulting in air being sucked in through it and over the filter.
Meantime, I am considering the UV light, just in case, and will replace filters a bit more often, to keep an eye on things.

P.S. We do normally see the humidity below 50% during the cooling season, but as the days get colder the unit runs less and we can get as high as 55-57%.

 

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