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The Goodman B1789888 Flow Check Piston Kit is the OEM refrigerant metering device (fixed-orifice piston) sized for the GSC130484BA 4-ton, 13 SEER air conditioner. The piston meters liquid refrigerant into the evaporator at the exact rate the system was designed for, which is critical to maintaining rated capacity, efficiency, and superheat.
Piston orifice diameter is matched to system tonnage to the thousandth of an inch. Installing a genuine Goodman OEM piston guarantees the correct bore size; a generic or mismatched piston will throttle refrigerant incorrectly, causing poor cooling, frosting, or compressor stress. OEM is the safe choice.
Advanced (4/5). Requires EPA Section 608 certification — recovering refrigerant, opening the liquid line at the piston housing, swapping the orifice, then evacuating and recharging the system. This is a job for a licensed HVAC technician.