The A/C Refrigerant Pressure Sensor’s main function is to allow the HVCA System (Heating, Ventilating and Air Conditioning) to adjust the internal temperature of the vehicle. This sensor converts the refrigerant pressure into an electrical value that is sent to the ECM (Engine Control Module) to determine the pressures and, consequently, activate or deactivate the compressor.
When the P0533 OBDII diagnostic code is stored, it is because the ECM found that the A/C Refrigerant Pressure Sensor “A” has a voltage above the allowable voltage.