Genuine Daikin 4025159 Compressor is the JT100G-VDL@T inverter scroll at the centre of the outdoor unit, its speed set by the inverter PCB to track load while an accumulator ahead of it traps liquid before it reaches the pump. When it fails the unit can no longer build head pressure, losing heating and cooling, and the inverter typically faults on overcurrent against a stalled rotor. The inverter PCB and accumulator are the parts most often renewed beside it, so it pays to have all three on the van before the job — and because this is the genuine Daikin scroll, it carries the right oil charge and winding for the inverter instead of leaving you to match a pattern unit by guesswork.