Fish Smell Coming from Central Air Conditioner

by Homeowner

(Long Island, New York)

All last summer a strong fish smell seemed to be coming from our mud room (no a/c vents in there, but there is a trap door in the ceiling to the attic which right next to it is the central air conditioner system). Adjacent to the mudroom is our den which has 2 a/c vents.





The smell is pretty strong in there too, although it seems stronger in the mudroom. We never figured out what the smell was and hoped it would just go away. The smell only came when we turned the a/c on and no other rooms (aside from the kitchen which is next to the den) got the smell.Today we turned on the central air conditioner unit for the first time of the season and it had the same horrible fish smell from last year. My husband went up into the attic, there was no smell by the a/c unit, the condensate pan did not smell either.Years ago we had a problem with the pan not emptying well enough due to the lack of incline and it would leak over the side through the garage ceiling. But it was corrected we think and has not leaked through the ceiling since.We were thinking today that maybe an animal got into the duct work to the den last summer and died (doesn't explain the mud room smelling though) so for lack of a better idea, my husband went to Home Depot and bought new ducts, which he replaced today.BUT, after the new ducts were in, we turned on the a/c and the smell was just as strong. We are out of ideas and hoping you may have a suggestion. Any insight will be much appreciated!Thanks so much.