There has been a sour/moldy smell coming out of the air vents in parts of my work building. It was worse in the summer, and actually caused me some eye irritation. When the smell would surface, the vents would be blowing humid air. Suggestions were a possible condensation leak. Now that the heat has been running and not the cold air, the smell is non-existent. However, the other day, we had a warm afternoon and as soon as the cold air started to blow, the smell began again. Any ideas on what can be causing this? I'm desperate for an answer as the guys who were called out to fix it couldn't find anything and I'm hoping they just weren't knowledgeable enough. I don't see my employer pursuing this unless I have some solid suggestions for a fix.