Hello, I have been dealing with flies in my apartment (first floor unit) since ~December 2022. I have identified them as fungus gnats. I originally thought they were coming from my bathroom ceiling fan as there was a leak there and I suspected mold, but my handyman opened up the ceiling and everything looked dry and normal. I have installed sticky fly traps with UV lights throughout my apartment and have so far caught hundreds of flies in every room. In the process of opening the ceiling, we put plastic sheets over the bathroom door, yet I am still catching plenty of flies, so now I know they are not originating solely from the bathroom. I am convinced they are coming from the vents, and in fact I have seen a few of them hanging out near the vents. I have a conventional central air system, and I hadn't been using heating/AC for 2-3 months, but I am running it continuously for a couple weeks to try and kill off the flies. I haven't replaced the filter since last September, but I will do that. Still, I think the flies must be breeding off some mold or moisture. How can I determine the source of the problem and remediate it? I have been told to inspect the blower motor for moisture/mold. Is there anything else I can inspect? Would installing screens in front of the vents help?