An assembly for selectively activating a cleaning fan of a combine harvester. The assembly includes a hydraulic pump for distributing power to the cleaning fan. The hydraulic pump is movably connected to a fixed point, and is configured to move between first and second positions. The hydraulic pump has an input portion for receiving power and a pressurized fluid port for distributing fluid to power the cleaning fan. A drive belt is wound about the input portion of the hydraulic pump and a drive pulley of the combine harvester. An actuator is provided for selectively moving the hydraulic pump between the first position, in which the drive belt is maintained in a state of tension such that the drive pulley can drive the cleaning fan, and the second position, in which the drive belt is maintained in a relaxed state such that the drive pulley cannot drive the cleaning fan.