Method for managing a thermal management device for a motor vehicle comprising a coolant circuit, in which a coolant is intended to circulate, said coolant circuit comprising: - a main loop comprising, in the direction of circulation of the coolant, a compressor, a condenser configured to exchange heat energy with a first element, a first expansion device and a first evaporator configured to exchange heat energy with a second element; - a bypass branch arranged parallel to the first expansion device and the first evaporator, said bypass branch comprising a second expansion device and a second evaporator arranged downstream of the second expansion device and configured to exchange heat energy with a third element, said thermal management device operating in a mode of strict cooling of the third element in which the condenser gives up heat energy to the first element and only the second evaporator absorbs heat energy from the third element, said management method comprising a step of managing the opening diameter of the first expansion device as a function of the ambient temperature such that coolant circulates inside the first evaporator, the opening diameter of the first expansion device decreasing as a function of the increase in the ambient temperature of the first element, said management method being characterized in that: - if the ambient temperature is above 25°C, the opening diameter of the first expansion device is of the order of 5% of its maximum opening diameter, - if the ambient temperature is less than or equal to 25°C, the opening diameter of the first expansion device is of the order of 200 of its maximum opening diameter. - a main loop comprising, in the direction of circulation of the coolant, a compressor, a condenser configured to exchange heat energy with a first element, a first expansion device and a first evaporator configured to exchange heat energy with a second element; - a bypass branch arranged parallel to the first expansion device and the first evaporator, said bypass branch comprising a second expansion device and a second evaporator arranged downstream of the second expansion device and configured to exchange heat energy with a third element, said thermal management device operating in a mode of strict cooling of the third element in which the condenser gives up heat energy to the first element and only the second evaporator absorbs heat energy from the third element, said management method comprising a step of managing the opening diameter of the first expansion device as a function of the ambient temperature such that coolant circulates inside the first evaporator, the opening diameter of the first expansion device decreasing as a function of the increase in the ambient temperature of the first element, said management method being characterized in that: - if the ambient temperature is above 25°C, the opening diameter of the first expansion device is of the order of 5% of its maximum opening diameter, - if the ambient temperature is less than or equal to 25°C, the opening diameter of the first expansion device is of the order of 200 of its maximum opening diameter. - if the ambient temperature is above 25°C, the opening diameter of the first expansion device is of the order of 5% of its maximum opening diameter, - if the ambient temperature is less than or equal to 25°C, the opening diameter of the first expansion device is of the order of 200 of its maximum opening diameter.