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The B1789871 is a genuine OEM refrigerant piston (flowrator) kit for Goodman ANZ130361AA heat pumps. This precision-machined metering orifice controls refrigerant flow into the evaporator or condenser coil, setting the system's superheat and ensuring proper heating and cooling capacity. A worn, clogged, or incorrectly sized piston causes poor performance, freeze-ups, and high energy use.
The OEM piston is bored to the exact orifice size specified for this tonnage, guaranteeing correct charge and superheat. Generic pistons in the wrong bore size will de-rate capacity or trip pressure faults.
Advanced (4/5). Requires recovering refrigerant, opening the liquid-line/piston housing, swapping the orifice, evacuating, and recharging. Licensed HVAC technician and EPA certification required.