Normally, freezers have electric heaters that are energized during the defrost cycle. Once out of the defrost cycle, the refrigeration system comes on but the fans do not. This allows the evap to cool off and to prevent circulating warm air from the heaters. This is controlled by a fan delay switch. It is a small, round device that can have 2, 3, or 4 wires going to it, depending on the manufacturer. It is usually clipped on to the end of the evap coil on one of the "U" bends, near the top, inside one of the ends of the evap. Usually where all the electrial components are located. It come in several variations, but it's main function is to prevent the fans from energizing too early. Usually does not bring fans on till evap hits 20 or so degrees. Check this out and get back to me.