The MRCOOL DIYCOUPLER-3858K75 Line Set Coupler Kit is an HVAC installation accessory designed to extend compatible 3/8-inch and 5/8-inch refrigerant line sets while including a 75-foot communication wire for seamless system connectivity. It works by securely joining two line sets, allowing greater installation flexibility between the outdoor condenser and indoor air handler in MRCOOL ... https://www.partshnc.com/mrcool-diycoupler-3858k75-line-set-coupler-kit