Whirlpool Refrigerator - Model: WRF757SDEM01 - First noticed it when the fan began hitting the built up ice. I replaced the fan and wire harness. Problem still exists. It took several weeks for the ice to build back up. The refrigerator and freezer seem to work fine as far as temperature. I put it into diagnostics today and ran the defrost test and the heater got hot and water runs into the pan. Do you have a suggestion as the next place to look?