Fungal nail infections can be caused by three different types of fungus, alone or in combination. 1  Dermatophytes are a type of fungus that can grow on the skin, hair, and nails. 2  They don't invade the deeper tissues of the body. 3  The most common dermatophyte, Trichophyton rubrum, causes most cases of athlete's foot.
Negative Airflow. Negative airflow is the opposite of postive airflow its having more exhaust fans then intake fans, this is good because its always taking new air into the case, but then you have more dust because the intake is mostly coming from gaps in the case and then causing trapped air.
I doubt it could be causing cold air in-flow as it is not external, and is before any vent controls. First question (simple one) - did you try switching the recirculated air on? With recirc on you should not have any outside air coming in. second question - Did you check to see where the air actually comes from? It could be a sealing issue on your door rather than from the vents; but you should be able to feel the airflow.