Abstract: The invention relates to a command device (13) of a fixed capacity compressor (9) associated with an evaporator through which an air flow passes in an air flow direction (6). The compressor (9) and the evaporator (12) are participating to an A/C loop (8) of an heating, ventilating and/or air conditioning device of a vehicle. The said command device (13) comprises a sensor (15,16) for the measurement of a measured value VM of a characteristic C of a fluid FR,A and comparison means (14) of the measured value VM of the characteristic C of the fluid FR,A with at least two step-values VSmin, VSmax of the characteristic C. The said command device (13) comprises an upstream temperature sensor (20) to be positioned upstream the evaporator (12) according to the air flow direction (6) to measure an upstream temperature T2 of the air flow (3) and give an information (18) which is taken into account by the said command device (13) in order to determine the said step-values VSmin, VSmax of the characteristic C.