Rudy5, I had the same exact problem with my bunk fan and looked in to the corrosion issue as it should be a relatively dry area. The drain tubes for condensation were clogged slightly causing about a 1/4 inch of water to build up in the filter box. It was an easy fix. Filled the box with more water than it was holding and bent the drain hoses under the cab with a broom handle until water that I put in would free flow out naturally with an even flow.