A system for cooling at least one component or part, said system comprising: - a heat exchange plate that comprises a coolant circulation duct and that is equipped, on the one hand, at the ends with connector elements (100A, 100B) each provided with a closure member and, on the other hand, a volume compensating device comprising a piston mounted able to slide sealably relative to the plate, between a first retracted position (figure 2) and a second forward position (figure 3) relative to the retracted position in which the volume available for the coolant in the duct is increased relative to its volume in the first position; - supply and/or discharge means (8, 82, 84, 300A, 300B) for the cooling duct, said means comprising connecting elements (300A, 300B) complementary to those of the plate for the connection and disconnection of the duct of the plate with a supply source and/or a coolant discharge line; characterized in that a member for keeping the piston in its retracted position is secured to at least a first complementary connector element of a first connector element of the plate, at least in translation along the fitting axis (X100A, X300A) thereof, and in that this maintaining member is capable of: - locking the piston in its first position when the first connector element of the plate and the first complementary connector element are coupled, and - keeping the piston in its first position, during the separation of the first connector element of the plate and the first complementary connector element, at least as long as the closure member of the first connector element of the plate is not in the position closing off an inner duct of that connector element. - a heat exchange plate that comprises a coolant circulation duct and that is equipped, on the one hand, at the ends with connector elements (100A, 100B) each provided with a closure member and, on the other hand, a volume compensating device comprising a piston mounted able to slide sealably relative to the plate, between a first retracted position (figure 2) and a second forward position (figure 3) relative to the retracted position in which the volume available for the coolant in the duct is increased relative to its volume in the first position; - supply and/or discharge means (8, 82, 84, 300A, 300B) for the cooling duct, said means comprising connecting elements (300A, 300B) complementary to those of the plate for the connection and disconnection of the duct of the plate with a supply source and/or a coolant discharge line; characterized in that a member for keeping the piston in its retracted position is secured to at least a first complementary connector element of a first connector element of the plate, at least in translation along the fitting axis (X100A, X300A) thereof, and in that this maintaining member is capable of: - locking the piston in its first position when the first connector element of the plate and the first complementary connector element are coupled, and - keeping the piston in its first position, during the separation of the first connector element of the plate and the first complementary connector element, at least as long as the closure member of the first connector element of the plate is not in the position closing off an inner duct of that connector element.