Arrived on site to troubleshoot an upstairs air handler with biological growth. The home has 3 systems in total. An American standard gas furnace / 4 ton AC that controls the main floor, a Mitsubishi mini split that controls a sunroom/living area and upstairs has a 2/2.5ton heat American standard heat pump. Upstairs does indeed have some biological growth on the evaporator and near the supply plenum. This can be attributed to extremely dirty duct work that is severly undersized. It’s 400cfm short on the supply side and 200cfm short on the supply side. We found the in line drain switch was only wired to shut off the condenser and would continue to run with standing water in the pan. We also discovered the 20x25x5” filter when the cabinets only calls for a 20x20x5” filter. Also a majority of the drain is original and wasn’t replaced during system replacement. It is poorly pitched and needs to be replaced for optimal slope. There are a few discrepancies pointing to the issues with the gr