[Radioactive]

In my experience freezing up is caused by not enough air flow (ie:dirty filter, not enough incoming air flow) if it used to work, that is my guess. The air in and out to the warehouse I don't think it maters on the freezing . It is probably more efficient to run closed loop because you are trying to cool the already pre or cooled air, it would take less energy to cool the already cooled air plus you get the benefit of removing the humidity and not introducing more moisture.