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The Goodman B1789882 Flowrator Piston Kit is the OEM refrigerant metering device engineered for the ASH130421AC 13 SEER heat pump condensing unit. This precision-machined restrictor piston (flowrator) controls refrigerant flow into the coil, ensuring correct superheat, subcooling, and rated cooling/heating capacity. Using the factory-spec orifice is critical — an incorrectly sized piston causes flooding, starving, poor efficiency, and premature compressor wear.
This is the genuine Goodman OEM piston, factory-calibrated to the exact bore diameter your system was designed around. Aftermarket universal piston assortments require you to identify and swap the correct orifice yourself — a common source of installer error. Choosing OEM removes the guesswork and protects your compressor warranty.
Moderate — HVAC technician recommended. Replacement requires recovering the refrigerant charge, opening the sealed system, brazing/flare access at the metering device, evacuation, and a full recharge to nameplate. EPA 608 certification is required to handle refrigerant. Not a DIY job for homeowners.