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The Goodman B1789857 is a genuine OEM piston (flowrator) kit for the ANZ130241AA heat pump. The piston is the fixed-orifice metering device that sets refrigerant flow into the coil. Matching the correct orifice size to the system is essential for proper superheat, capacity, and efficiency — a wrong or worn piston causes poor cooling, high energy use, or coil frosting.
The genuine OEM piston is bored to the exact orifice diameter this system was engineered for. Generic pistons are sold in size ranges and are easy to mis-select; even one size off will throw off superheat and capacity. For a metering device, matching the OEM part number removes all guesswork.
Professional / EPA-certified only. Access requires recovering refrigerant, opening the liquid-line/piston housing, replacing the piston and seals, then evacuating and recharging. EPA Section 608 certification is required by law. Buy the correct OEM piston and have a licensed technician install it.