Genuine Daikin 1423839 Stop Valve Assembly (Liquid Line) is the liquid-line stop valve in the outdoor unit that isolates the refrigerant circuit at the liquid service port for installation and servicing. When it leaks or seizes, the unit can lose refrigerant, lose output, or be difficult to service safely. A genuine valve seals and operates the way your Daikin expects — where a non-genuine part can leak or seize.