A method of detecting a loss of a refrigerant from a refrigerant circuit comprising at least one condenser , at least one compressor , and at least one evaporator having an outlet port, and at least one expansion valve having an inlet port and an outlet port, the refrigerant circuit also comprising a first sensor for recording a thermodynamic state of the refrigerant at the inlet port of the at least one expansion valve and/or a thermodynamic state of the refrigerant at or near the at least one condenser , and a second sensor for recording a thermodynamic state of the refrigerant at the outlet port of the at least one evaporator , the method comprising the steps of: recording a first signal indicative of a thermodynamic state of the refrigerant using the first sensor ; recording a second signal indicative of a thermodynamic state of the refrigerant using the second sensor ; characterised in that the method comprises the steps of determining a first value of maximum available capacity of the refrigerant circuit as a function of the first and second signals; recording a third signal, the third signal being - a signal indicative of power currently dissipated by the at least one evaporator ; determining a first value of current capacity of the refrigerant circuit as a function of the third signal; determining a first ratio by relating the first value of current capacity to the first value of maximum available capacity; and if the determined first ratio exceeds one by a first threshold: producing a first alarm signal indicative of the loss of the refrigerant; further characterised in that the refrigerant circuit comprises another sensor associated with the at least one evaporator ; the method further comprising the step of: recording the signal indicative of power currently dissipated by the at least one evaporator using the other sensor . recording a first signal indicative of a thermodynamic state of the refrigerant using the first sensor ; recording a second signal indicative of a thermodynamic state of the refrigerant using the second sensor ; characterised in that the method comprises the steps of determining a first value of maximum available capacity of the refrigerant circuit as a function of the first and second signals; recording a third signal, the third signal being - a signal indicative of power currently dissipated by the at least one evaporator ; - a signal indicative of power currently dissipated by the at least one evaporator ; determining a first value of current capacity of the refrigerant circuit as a function of the third signal; determining a first ratio by relating the first value of current capacity to the first value of maximum available capacity; and if the determined first ratio exceeds one by a first threshold: producing a first alarm signal indicative of the loss of the refrigerant; further characterised in that the refrigerant circuit comprises another sensor associated with the at least one evaporator ; the method further comprising the step of: recording the signal indicative of power currently dissipated by the at least one evaporator using the other sensor . producing a first alarm signal indicative of the loss of the refrigerant; further characterised in that the refrigerant circuit comprises another sensor associated with the at least one evaporator ; <EOS>