Method for operating a coolant circuit of a refrigeration system of a vehicle, having - at least two system sections (1.1, 1.2), in particular a low-pressure system section (1.1) and a high-pressure system section (1.2), in each of which a system operating state can be set, by means of a controller, with respect to the pressure and temperature of the coolant, - a pressure sensor (p HD, p HD ', p ND, p ND ', p ND ") arranged in each system section (1.1, 1.2), wherein the sensor signals of the pressure sensors (p HD, p HD ', p ND, p ND ', p ND ") are transmitted to the controller in order to control or regulate the refrigeration system, - heat exchangers (2, 3, 6) arranged in the system sections (1.1, 1.2) as components of the coolant circuit, wherein coolant is conveyed from the low-pressure system section (1.1) into the high-pressure system section (1.2) by a coolant compressor as a further component of the coolant circuit, wherein - in order to control or regulate at least one component (2, 3, 5, 6) by means of the controller, a temperature sensor for detecting the coolant temperature at the outlet of the component is connected downstream thereof, - the sensor signal of the temperature sensor is transmitted to the controller, - an approximate pressure value (p HD_Kond/GK, p HD_KMV) at the position of the temperature sensor is calculated using a pressure loss value (Δp, Δp CH, Δp IWT, Δp IWT/R1, Δp VERD, Δp VERD/R1, Δp Kond/GK) which is determined using a pressure loss calculation function, starting from the position of the pressure sensor (p HD, p HD ', p ND, p ND ', p ND ") arranged in the system section (1.1, 1.2) of the components (2, 3, 5, 6) up to the position of the temperature sensor if the temperature sensor and the pressure sensor (p HD, p HD ', p ND, p ND ', p ND ") are arranged at different positions in the system section (1.1, 1.2), - the pressure loss calculation function is provided by calculating the currently conveyed coolant mass flow (m KM_berechnet) from the operating data of the coolant compressor and, by means of a mass flow-pressure loss characteristic curve which is calculated as a function of the currently conveyed mass flow (m KM_berechnet) and the geometry data of the relevant line section between the position of the pressure sensor (p HD, p HD ', p ND, p ND ', p ND ") and the position of the temperature sensor and the component (2, 3, 5, 6), the pressure loss between the position of the pressure sensor (p HD, p HD ', p ND, p ND ', p ND ") and the position of the temperature sensor, a corresponding pressure loss value (Δp, Δp CH, Δp IWT, Δp IWT/R1, Δp VERD, Δp VERD/R1, Δp Kond/GK) is determined, and - the refrigeration system is controlled or regulated at least as a function of the calculated approximate pressure value (p HD_Kond/GK, p HD_KMV, p ND_CH, p ND_IWT). - at least two system sections (1.1, 1.2), in particular a low-pressure system section (1.1) and a high-pressure system section (1.2), in each of which a system operating state can be set, by means of a controller, with respect to the pressure and temperature of the coolant, - a pressure sensor (p HD, p HD ', p ND, p ND ', p ND ") arranged in each system section (1.1, 1.2), wherein the sensor signals of the pressure sensors (p HD, p HD ', p ND, p ND ', p ND ") are transmitted to the controller in order to control or regulate the refrigeration system, - heat exchangers (2, 3, 6) arranged in the system sections (1.1, 1.2) as components of the coolant circuit, wherein coolant is conveyed from the low-pressure system section (1.1) into the high-pressure system section (1.2) by a coolant compressor as a further component of the coolant circuit, wherein - in order to control or regulate at least one component (2, 3, 5, 6) by means of the controller, a temperature sensor for detecting the coolant temperature at the outlet of the component is connected downstream thereof, - the sensor signal of the temperature sensor is transmitted to the controller, - an approximate pressure value (p HD_Kond/GK, p HD_KMV) at the position of the temperature sensor is calculated using a pressure loss value (Δp, Δp CH, Δp IWT, Δp IWT/R1, Δp VERD, Δp VERD/R1, Δp Kond/GK) which is determined using a pressure loss calculation function, starting from the position of the pressure sensor (p HD, p HD ', p ND, p ND ', p ND ") arranged in the system section (1.1, 1.2) of the components (2, 3, 5, 6) up to the position of the temperature sensor if the temperature sensor and the pressure sensor (p HD, p HD ', p ND, p ND ', p ND ") are arranged at different positions in the system section (1.1, 1.2), - the pressure loss calculation function is provided by calculating the currently conveyed coolant mass flow (m KM_berechnet) from the operating data of the coolant compressor and, by means of a mass flow-pressure loss characteristic curve which is calculated as a function of the currently conveyed mass flow (m KM_berechnet) and the geometry data of the relevant line section between the position of the pressure sensor (p HD, p HD ', p ND, p ND ', p ND ") and the position of the temperature sensor and the component (2, 3, 5, 6), the pressure loss between the position of the pressure sensor (p HD, p HD ', p ND, p ND ', p ND ") and the position of the temperature sensor, a corresponding pressure loss value (Δp, Δp CH, Δp IWT, Δp IWT/R1, Δp VERD, Δp VERD/R1, Δp Kond/GK) is determined, and - the refrigeration system is controlled or regulated at least as a function of the calculated approximate pressure value (p HD_Kond/GK, p HD_KMV, p ND_CH, p ND_IWT).