Method for controlling a thermal conditioning system for a motor vehicle comprising a refrigerant circuit configured to circulate a refrigerant, the refrigerant circuit comprising: - A main loop comprising successively, in the direction of flow of the refrigerant: a compression device, a condenser configured to exchange heat with a first heat transfer fluid, a first expansion device, a first evaporator configured to exchange heat with a second heat transfer fluid, a second expansion device, - A bypass branch connecting a first connection point positioned on the main loop between the condenser and the first expansion device to a second connection point positioned on the main loop between the second expansion device and the compression device, the bypass branch comprising successively, in the direction of flow of the refrigerant, a third expansion device and a second evaporator configured to exchange heat with a third heat transfer fluid, the thermal conditioning system being configured so that the temperature (T1_mes) of the second heat transfer fluid at the outlet of the first evaporator reaches a temperature setpoint (T1_cons) and so that the temperature (T2_mes) of the third heat transfer fluid at the outlet of the second evaporator reaches a temperature setpoint (T2_cons), the control method comprising the following steps: - Receiving a priority request giving priority either to cooling the second heat transfer fluid or to cooling the third heat transfer fluid (step 50), - If the thermal power required in order to simultaneously reach the temperature setpoint of the second heat transfer fluid and of the third heat transfer fluid is greater than the thermal power supplied jointly by the first evaporator and the second evaporator, increasing the rotation speed of the compression device (step 51), the method being characterized in that it comprises the following steps: - If the rotation speed of the compression device has reached a predetermined maximum value (N_max) and if priority is given to cooling the third heat transfer fluid: Calculating a modified temperature setpoint (T1_mod) of the second heat transfer fluid at the outlet of the first evaporator, greater than the acquired temperature setpoint (T1_cons) (step 52), Adjusting a refrigerant flow area through the second expansion device so that the temperature of the second heat transfer fluid reaches the modified temperature setpoint (T1_mod) (step 53), increasing the modified temperature setpoint (T1_mod) of the second heat transfer fluid until the temperature (T2_mes) of the third heat transfer fluid reaches the temperature setpoint (T2_cons) (step 54). - A main loop comprising successively, in the direction of flow of the refrigerant: a compression device, a condenser configured to exchange heat with a first heat transfer fluid, a first expansion device, a first evaporator configured to exchange heat with a second heat transfer fluid, a second expansion device, a compression device, a condenser configured to exchange heat with a first heat transfer fluid, a first expansion device, a first evaporator configured to exchange heat with a second heat transfer fluid, a second expansion device, - A bypass branch connecting a first connection point positioned on the main loop between the condenser and the first expansion device to a second connection point positioned on the main loop between the second expansion device and the compression device, - Receiving a priority request giving priority either to cooling the second heat transfer fluid or to cooling the third heat transfer fluid (step 50), - If the thermal power required in order to simultaneously reach the temperature setpoint of the second heat transfer fluid and of the third heat transfer fluid is greater than the thermal power supplied jointly by the first evaporator and the second evaporator, increasing the rotation speed of the compression device (step 51), the method being characterized in that it comprises the following steps: - If the rotation speed of the compression device has reached a predetermined maximum value (N_max) and if priority is given to cooling the third heat transfer fluid: Calculating a modified temperature setpoint (T1_mod) of the second heat transfer fluid at the outlet of the first evaporator, greater than the acquired temperature setpoint (T1_cons) (step 52), Adjusting a refrigerant flow area through the second expansion device so that the temperature of the second heat transfer fluid reaches the modified temperature setpoint (T1_mod) (step 53), increasing the modified temperature setpoint (T1_mod) of the second heat transfer fluid until the temperature (T2_mes) of the third heat transfer fluid reaches the temperature setpoint (T2_cons) (step 54). Calculating a modified temperature setpoint (T1_mod) of the second heat transfer fluid at the outlet of the first evaporator, greater than the acquired temperature setpoint (T1_cons) (step 52), Adjusting a refrigerant flow area through the second expansion device so that the temperature of the second heat transfer fluid reaches the modified temperature setpoint (T1_mod) (step 53), increasing the modified temperature setpoint (T1_mod) of the second heat transfer fluid until the temperature (T2_mes) of the third heat transfer fluid reaches the temperature setpoint (T2_cons) (step 54).