outdoor unit (of an air conditioner or heat pump)
Refers specifically to the external component of a split-system air conditioner or heat pump, containing the compressor and condenser.
The outdoor unit of the air conditioner is noisy.
室外機の上に物を置かないでください。
Please do not put things on top of the outdoor unit.
Compound of 室外 (shitsugai, 'outdoors') + 機 (ki, 'machine, device').