I own a commercial office space, a small one, in North GA. It is a one ton unit. I had some white powder coming from the evaporator coil through the ducts and onto the desks and floors. I had the entire unit replaced and 1 year later it came back. I have checked all the obvious things. I have replaced duct work, replaced filters, checked returns, in addition to replacing the air handler and A coil. My HVAC guy has asked numerous experts in the field including a Goodman tech without any help. At this point we are trying to clean the coil and hope it doesn't come back. So far those attempts have yet to be successful. Ever seen this? Any idea what it is? It is a white powder and not building materials or paper. It forms on the coil the office space is very clean an nothing to my knowledge is being sucked into the unit.