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The Lennox 59W21 (OEM reference 100679-35) is a genuine R410A thermostatic expansion valve rated at 92+2 Psig, engineered to deliver precise refrigerant metering for consistent and efficient system performance in compatible Lennox equipment. Symptoms of a failing expansion valve include insufficient cooling, frost buildup on the evaporator coil, fluctuating suction line pressures, and compressor short cycling. This OEM Lennox part ensures a factory-fit replacement that restores proper refrigerant flow and system reliability.