A method for controlling an inlet-adjustment mechanism in an air inlet for a compressor so as to switch the mechanism in a binary fashion between two positions P1 and P2 for adjusting a flow area of the inlet. The method includes identifying a threshold line on a compressor map of pressure ratio versus corrected flow rate for the compressor. The threshold line is a line on which the pressure ratio and flow rate of the compressor are the same for the P1 and P2 positions of the inlet-adjustment mechanism at equal speeds. When the operating point of the compressor on the compressor map crosses the threshold line, the inlet-adjustment mechanism is switched from one of its binary positions to the other.