The Resideo L4064B2228/B Fan & Limit Controller is a temperature-sensing control designed to manage blower operation and provide high-temperature protection in compatible heating systems. It monitors furnace temperature and activates the blower when the selected fan-on setting is reached, then stops it as the temperature drops. Its limit function helps prevent overheating by interrupt... https://www.partshnc.com/resideo-l4064b2228-b-5-fan-and-limit-controller-insert