My 9 yr. Old Lennox AC suddenly froze up July 1. Found the filter clogged with what looked like black charcoal. Replaced filter and unit worked great for two weeks. Found filter again clogged with the same black substance. Repair man checked the duct work and vacuumed the A frame and Return air space beneath the unit. Two weeks later the filter is black again. Where could this material be coming from? It is not wet and I would think it would have to come from beneath the unit since the filter is the only thing that appears black. Carpet and grillwork do not appear to be contaminated.

Nancy

Your filter will pick up any thing inside the home. The black residue may not be from the duct work but from something inside the home. Some scented candles put of a lot of carbon black. Are you burning candles or some open flame inside the home?

I asked my renter about candle usage. She says she rarely uses candles, then only in the master bath for maybe an hour. Says it has been over a month since anything in the kitchen smoked enough to set off the smoke alarm. It is still a mystery to me.

Nancy