Genuine Daikin 138181J Motorised Expansion Valve Coil is the electrical coil that drives the motor-operated expansion valve, moving it to the position the control board calls for to meter refrigerant flow. When it fails, the valve may not move correctly and the unit can lose output, heat or cool poorly, or stop and start at odd times. A genuine coil drives the valve the way your Daikin expects, keeping flow control accurate — where a non-genuine part can drive it weakly or unreliably.