Been having trouble with this too and have replaced more or less everything or at least tried different components. I have an error when a pressure change is requested the accumulator pressure remains constant but changed valve block, control unit and sensor on accumulator and compressor. Have just noticed on autologic that 3 of my sensors when I push down on car voltage goes down but the front left goes up opposite to the other three so just replace the sensor and its still opposite with the voltage going up not down. Does anyone have any ideas or know what there voltages do when the sensor moves

__________________
2005 X5 4.8is - 1995 Discovery 300tdi - 1970 Series IIa - 2004 CCM 644DS -2000 ZX12r