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The Goodman B1789852 is a genuine OEM refrigerant metering piston kit sized for the ASH130181AB heat pump. Also called a flow-rater, this fixed-orifice piston meters liquid refrigerant into the evaporator or condenser coil at the exact rate required to match the system's rated capacity. A correctly sized piston is essential for proper superheat, subcooling, and efficiency.
Piston bore diameter is matched to the tonnage of your specific unit. An OEM Goodman piston guarantees the correct orifice size for the ASH130181AB, while a mismatched generic piston can starve or flood the coil, cutting capacity and driving up energy use. When in doubt, always match OEM.
The piston seats inside the metering-device housing at the coil connection. Access typically requires recovering refrigerant and opening the flare/braze union, then pulling a vacuum and recharging. Best handled by an EPA-certified technician.