Outdoor mounted controllers: Leave the power on and the dial / switch in the "OFF" position. The heat from the transformer will keep the enclosure warm enough to keep condensation from forming inside the controller enclosure. The dial in the "OFF" position will keep the controller from activating the solenoids in the field. Indoor mounted controllers: Leave the power on and the dial / switch in the "OFF" position. This will prevent the controller from activating the solenoids in the field. Rain Sensors: There is very little winter preparation required for rain sensors. If your sensor is the type with a cup or bowl that catches water, you might want to remove the water and place a plastic bag over the sensor. This will keep any water from accumulating and freezing in the cup or bowl area. Learn more here: https://www.hunterindustries.com/support/pro-c-winterizing-your-system