said by builderbob :annual PM should include a couple of "blue" tablets in the condensate line at the attic coil.
A/C-Safe brand, 6 tablets for $2.97, sku 380163 @ HD.
Actually, if you stuff them into the line then maybe they will plug the line?
It seems they should be tossed-in to the pan under the A-coil, but IIRC there's no easy/trivial way to get at that pan on my fan coil units. Maybe I should cut an access panel so it's easy to toss one-in there once a season...?