Supermarket Drain pan not level, overflowing and running back down the ductwork. Major mold infestation. Supermarket Pigeons entering the outside air ductwork and nesting. Hospital Bathroom exhaust fan tied to return on AC system. Fecal coliform found in the AC ductwork.
Hospital Remains of sandwich left by worker found in ductwork.
Ham and cheese we think. Major mold infestation School Duct sealant applied on the inside of the duct next to the reheat coils. Major mold due to humidity problems. These are just a few problems that could have been avoided. Posts on this thread, including this one Aspergillus.