I got me Pro-Face PLC back from the manufacturer today. I had posted about the failure a few weeks ago. It turns out that there was some sort of corrosion on the main board and the video board. The PLC is in a gasketed enclosure with three Greenfield cables coming in. The machine or the control box never got wet and there is nothing in the air. The heat goes from 65 day to 55 night with overhead gas furnaces. Could just the Greenfield be letting moisture in? How do I prevent it from happening again? A light bulb running all the time? A vent fan? Maybe the thing shouldn't be that well sealed?
Here are some pix of the PLC, and enclosure.