The Lennox 17K54 Outdoor Temperature Sensor is a replacement sensing component designed to monitor outdoor air temperature in compatible Lennox HVAC systems. It detects temperature changes and sends corresponding electrical signals to the system’s control board, enabling accurate adjustment of heating and cooling operation. Used with compatible furnaces, heat pumps, air conditioners, ... https://www.partshnc.com/lennox-17k54-t4-outdoor-temperature-sensor