The Lennox Y8737 is a thermal expansion valve (TXV) designed for use in HVAC systems that utilize R410A refrigerant, a common coolant in air conditioners. Unlike valves controlling water flow, TXVs are self-regulating. They use a sensor to monitor refrigerant temperature within the system. By responding to temperature changes, the TXV automatically adjusts the flow of refrigerant. https://www.partshnc.com/y8737-lennox-txv-35-5ton-sanhua