The invention relates to a method for operating a refrigeration system of a vehicle with a refrigerant circuit (1.1) having a cooling and heating function, in which a refrigerant compressor (2), a high-pressure heat exchanger (3) and an expansion element (AE1, AE2) of a refrigerant be flowed through, the heating function is realized by using the waste heat of the refrigerant compressor (2), a supply air flow (L1) is heated by means of the high-pressure heat exchanger, and the following process steps are carried out: a) running up the refrigerant compressor (2) up to an initial speed, b) determining a control difference (R diff, t ) between a desired value and an actual value of a discharge temperature (T) of the supply air flow (L1), c) determining the speed (n KMV ) of the refrigerant compressor (2), and either c1) closing of the expansion element (AE1, AE2), if at a maximum speed value (n KMV, max ) of the refrigerant compressor (2), the low pressure (p ND ) of the refrigerant circuit (1.1) is greater than a minimum low pressure value (p ND, min ) , or c2) increasing the speed (n KMV ) of the refrigerant compressor (2) at a speed (n KMV ) of the refrigerant compressor (2) smaller than the maximum speed value (n KMV, max ) and opening the expansion device (AE1, AE2) when the low pressure (P ND ) reaches the minimum low pressure value (p ND, min ), and d) repeating the process steps b and c until no control difference (R diff, t ) is measurable or the low pressure (p ND ) has reached the minimum low pressure value (p ND, min ).
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