Method for maximizing refrigerant in active system sections of a refrigeration system, refrigeration system and motor vehicle with such a refrigeration system

Abstract

Method (500) for operating a refrigeration system (10) for a motor vehicle, wherein the refrigeration system (10) comprises: a refrigerant compressor (12) which is or can be connected to a primary branch (14) and a secondary branch (16); a directly or indirectly acting external heat exchanger (18) which is arranged in the primary branch (14); an evaporator (22) which is arranged in the primary branch (14); at least one further heat exchanger which represents a heat source, in particular a heating register (26), which is arranged in the secondary branch (16); a primary branch valve (A4) arranged between the refrigerant compressor (12) and the external heat exchanger (18); a secondary branch valve (A3) arranged between the refrigerant compressor (12) and the further heat exchanger which represents a heat source, in particular a heating register (26);at least one valve device (A2, A5) arranged between a high-pressure side section (15, 15a) of the primary branch (14) or the secondary branch (16) and a low-pressure side line section located upstream of the refrigerant compressor (12), wherein the method (500) comprises the following steps: setting (S502) an operating mode of the refrigeration system with an active primary branch (14) and an inactive secondary branch (16) or with an active secondary branch (16) and an inactive primary branch (14); characterized by detecting (S503) the pressure (p_inak) in the inactive branch (14, 16); activating a suction of refrigerant from the inactive branch (14, 16) into the active branch (14, 16) by lowering (S506) the pressure (pA) in the active branch (14, 16) to a value below the pressure (p_inak) in the inactive branch (14, 16) and by opening the relevant valve device (A2, A5).;

Description

[0001] The invention relates to a method for maximizing refrigerant in active system sections of a refrigeration system for a motor vehicle, a refrigeration system and a motor vehicle with such a refrigeration system.

[0002] A refrigeration system, which in particular can also have a heat pump function, usually comprises a refrigerant compressor that is or can be connected to a primary branch and a secondary branch; a directly or indirectly acting external heat exchanger that is arranged in the primary branch; an evaporator that is arranged in the primary branch; at least one further heat exchanger that acts as a heat source, in particular a heating register, that is arranged in the secondary branch; a primary branch valve arranged between the refrigerant compressor and the external heat exchanger; a secondary branch valve arranged between the refrigerant compressor and the at least one further heat exchanger, in particular a heating register.

[0003] Refrigeration systems in which refrigerant can flow from an inactive area or line into an active area or line are known, for example, from DE 10 2011 118 162 A1 or DE 10 2019 201 427 A1. DE 10 2013 019 498 A1 describes a refrigeration system in which calculation models are used for refrigerant management. In these known refrigeration systems, the removal of refrigerant from an inactive area occurs due to the working pressures typically occurring during operation, without this aspect being given particular importance.

[0004] In addition, reference is made to the documents DE 10 2013 021 360 A1 and DE 10 2017 218 424 A1, from which refrigeration systems according to the preamble of claim 7 are known.

[0005] It has been shown that in refrigeration systems operated as described in the prior art documents mentioned, the active refrigerant quantity may be insufficiently monitored, so that cases may occur in which the refrigeration system or the system may be operated underfilled (in the active area or line), which may lead to losses in the performance of the refrigeration system in the various operating states.

[0006] The object underlying the invention is to provide a method in which the refrigerant management is optimized, in particular taking into account different operating states of the refrigeration system.

[0007] This problem is solved by a method, a refrigeration system, and a motor vehicle having the features of the respective independent patent claims. Advantageous embodiments with useful further developments are specified in the dependent patent claims.

[0008] A method is therefore proposed for operating a refrigeration system for a motor vehicle, the refrigeration system comprising: a refrigerant compressor which is connectable or connected to a primary line and a secondary line; a directly or indirectly acting external heat exchanger which is arranged in the primary line; an evaporator which is arranged in the primary line; at least one further heat exchanger which represents a heat source, in particular a heating register, which is arranged in the secondary line; a primary line valve arranged between the refrigerant compressor and the external heat exchanger; a secondary line valve arranged between the refrigerant compressor and the further heat exchanger which represents a heat source, in particular a heating register.at least one valve device arranged between a high-pressure side section of the primary line or the secondary line and a low-pressure side line section located upstream of the refrigerant compressor; This includes the following steps:

[0009] Setting an operating mode of the refrigeration system with an active primary line and an inactive secondary line or with an active secondary line and an inactive primary line; detecting the pressure in the inactive line; activating a refrigerant extraction from the inactive line into the active line by reducing the pressure in the active line to a value below the pressure in the inactive line and by opening the relevant valve device.

[0010] By detecting the pressure in the inactive line or section of the refrigeration system, the activation of a refrigerant extraction from the inactive line can be specifically implemented, whereby a reduction in the pressure in the active line can be specifically implemented. Please note that the term "detection or recording of pressure" used here can refer to a direct pressure measurement or an indirect estimation of the pressure, in particular based on other parameters, such as refrigerant temperature, refrigerant properties, or other operating parameters of the refrigeration system, e.g., the refrigerant compressor. The term "detection / recording" therefore refers to obtaining a pressure value, which can be based on a specific measurement or which can be derived, calculated, or estimated using other key figures.

[0011] The process allows the pressure in the active line to be reduced from a working pressure level that is higher than the pressure in the inactive line. This makes it possible to reduce the pressure in the active line, at least temporarily, so much that refrigerant can be extracted from the inactive line to maximize the refrigerant quantity in the active section of the refrigeration system, before subsequently returning to the actual working pressure level.

[0012] In this process, the pressure in the active branch can be further reduced from a working pressure level that is lower than the pressure in the inactive branch. This makes it possible to further reduce the pressure in the active branch, at least temporarily, in order to accelerate the removal of refrigerant from the inactive branch or to maximize the amount of refrigerant in the active region.

[0013] In order to ensure the operation of the refrigeration system and its performance in all cases when the recovery of refrigerant from the inactive line is activated, the pressure in the active line can be maintained at a pressure level that corresponds to a low pressure limit permissible for the refrigeration system.

[0014] In the method, the pressure value detected or estimated in the inactive line can be compared with the static pressure occurring at the prevailing ambient temperature or the prevailing coolant / fluid temperature, wherein the activation of the evacuation of refrigerant from the inactive line occurs when the detected pressure is greater than or equal to the static pressure occurring at the ambient temperature.

[0015] The need for extraction can be determined, detected, or predicted, in particular, using pressure sensors mounted in the inactive branch or dead volume. If the pressure value recorded in these inactive branches or segments is (permanently) below the static pressure that occurs at ambient temperature or coolant / fluid temperature, then this branch has already been extracted and only refrigerant is present in the gas phase. If the pressure value recorded in these inactive branches or segments is at or above the static pressure that occurs at the respectively recorded or measured ambient temperature or coolant / fluid temperature, then this branch or sector has not yet been extracted and the refrigerant is present as a two-phase mixture or, under certain circumstances, even in liquid form. The relationship between (ambient / fluid) temperature and refrigerant pressure can be derived, for example, from a material data table for a refrigerant used.

[0016] This process allows for activating the recovery of refrigerant from the inactive line when the refrigeration system is started or restarted to maximize the refrigerant quantity in the active line. This makes it possible to quickly bring the refrigeration system to optimal performance in a specific operating mode and positively influence the refrigerant quantity in the active line right from the start of operation.

[0017] A refrigeration system, in particular with a heat pump function, for a motor vehicle is also proposed, the refrigeration system comprising: a refrigerant compressor which is connectable or connected to a primary line and a secondary line; a directly or indirectly acting external heat exchanger which is arranged in the primary line; an evaporator which is arranged in the primary line; at least one further, a heat exchanger representing a heat source, in particular a heating register, which is arranged in the secondary line; a primary line valve arranged between the refrigerant compressor and the external heat exchanger; a primary line valve arranged between the refrigerant compressor and the further, a secondary branch valve arranged in a heat exchanger representing a heat source, in particular a heating register; at least one valve device arranged between a high-pressure side section of the primary branch or the secondary branch and a low-pressure side line section located upstream of the refrigerant compressor; and at least one pressure sensor or pressure / temperature sensor arranged in the relevant high-pressure side section of the primary branch or the secondary branch and configured to detect the pressure in the inactive branch in an operating state with an active primary branch and an inactive secondary branch or with an active secondary branch and an inactive primary branch, wherein the refrigeration system comprises a control device configured to carry out the method described above.

[0018] A motor vehicle, in particular an at least partially electrically powered motor vehicle, can have a refrigeration system as described above. In an electric vehicle, the efficient operation of the refrigeration system can lead to electricity savings, thus enabling a greater range of the electric vehicle.

[0019] It should be noted that the method described above can be used for any type of refrigeration system that has a system with segmentable sections. The method can therefore be used both for a pure refrigeration system and for a system with a heat pump and / or reheat function, so that the associated advantages can be exploited in a positive and targeted manner. The simplest variant, for example, can be seen as a refrigeration system that has a second evaporator line in the form of a chiller or air-fed evaporator, whereby the additional or second line can be represented in a segmentable manner.

[0020] Further advantages and details of the invention will become apparent from the following description of embodiments with reference to the figures. Fig. 1 a schematic and simplified circuit diagram of a refrigeration system for a motor vehicle, Fig. 2 a flowchart of an exemplary implementation of the method, in particular by means of the Fig. 1 described refrigeration system.

[0021] In Fig. 1 shows a schematic and simplified representation of an embodiment of a refrigeration system 10 for a motor vehicle. The refrigeration system 10 comprises a refrigerant circuit 11, which can be operated both in refrigeration system mode (also referred to as AC mode for short) and in heat pump mode. In the embodiment shown, the refrigeration system 10 comprises a refrigerant compressor 12, an external heat exchanger 18, an internal heat exchanger 20, an evaporator 22, and an accumulator or refrigerant collector 24. The external heat exchanger 18 can be designed as a condenser or gas cooler. In particular, the external heat exchanger 18 can be bidirectionally flowed through in the embodiment shown.

[0022] The evaporator 22 is shown here as an example of a front evaporator for a vehicle. The evaporator 22 also represents other possible evaporators in a vehicle, such as rear evaporators, which can be arranged parallel to one another in terms of flow. In other words, the refrigeration system 10 comprises at least one evaporator 22.

[0023] A shut-off valve A4 is located downstream of the compressor 12. An expansion valve AE2 is provided upstream of the evaporator 22.

[0024] For the purposes of this description, in the entire refrigerant circuit 11 of the refrigeration system 10, the section from the compressor 12 to the external heat exchanger 18, to the internal heat exchanger 20 and to the evaporator 22 is referred to as the primary line 14.

[0025] The refrigeration system 10 further comprises a heating register 26 (also referred to as a heating condenser or hot gas cooler). A shut-off valve A3 is arranged upstream of the heating register 26. A shut-off valve A1 is arranged downstream of the heating register 26. Furthermore, an expansion valve AE4 is arranged downstream of the heating register 26.

[0026] For the purposes of this description, the section of the entire refrigerant circuit of the refrigeration system 10 from the compressor 12 to the heating register 26, to the expansion valve AE4, and to a branch Ab2 is referred to as the secondary branch 16. The secondary branch 16 comprises a heating branch 16.1, which extends from the shut-off valve A3 via the heating register 26 to the shut-off valve A1. Furthermore, the secondary branch 16 comprises a reheat branch 16.2, which is fluidly connected upstream to the heating register 26 and downstream to the external heat exchanger 18. The secondary branch 16 or the reheat branch 16.2 flows into the primary branch 14 at a branch point Ab2.

[0027] The refrigeration system 10 includes a further evaporator or chiller 28. The chiller 28 is arranged in parallel flow with the evaporator 22. The chiller 28 can be used, for example, to cool an electrical component of the vehicle, but also to implement a water heat pump function by utilizing the waste heat from at least one electrical component. An expansion valve AE1 is connected upstream of the chiller 28.

[0028] The refrigeration system 10 can also include an electric heating element 30, which is designed, for example, as a high-voltage PTC heating element. The electric heating element 30 serves as an additional heater for an air supply flow L directed into the vehicle interior. The electric heating element 30 can be housed together with the heating register 26 and the evaporator 22 in an air conditioning unit 32. The electric heating element 30 can be arranged downstream of the heating register 26.

[0029] In the Fig. 1 also shows check valves R1 and R2. Furthermore, several sensors pT1 to pT5 are shown for measuring the pressure and / or temperature of the refrigerant. It should be noted that the number of sensors and their arrangement are shown here only as examples. A refrigeration system 10 can also have fewer or more sensors. In the example shown, combined pressure / temperature sensors pT1 to pT5 are shown as sensors. However, it is equally conceivable that separate sensors are used to measure pressure or temperature and, if necessary, are arranged spatially separated from one another along the refrigerant lines.

[0030] The refrigeration system 10 can be operated in different modes, which are briefly described below.

[0031] In AC operation of the refrigerant circuit 11, the refrigerant compressed to high pressure flows from the refrigerant compressor 12 with the shut-off valve A4 open into the external heat exchanger 18. From there, it flows to the high-pressure section of the internal heat exchanger 20 and the fully open expansion valve AE3. Via a branch point Ab1, the refrigerant can flow to the expansion valve AE2 and into the interior evaporator 22 (evaporator section 22.1). In parallel or alternatively, the refrigerant can flow via a branch point Ab4 and the expansion valve AE1 into the chiller 28 (chiller section 28.1). From the evaporator 22 and / or the chiller 28, the refrigerant flows on the low-pressure side into the receiver 24 and through the low-pressure section of the internal heat exchanger 20 back to the compressor 12.

[0032] In AC operation, the heating branch 16.1 or the secondary branch 16 is shut off by means of the shut-off valve A3, so that hot refrigerant cannot flow through the heating register 26. To retrieve refrigerant from the inactive heating branch 16.1, the shut-off element A5, designed as a shut-off valve, can be opened so that the refrigerant can flow towards the collector 24 via the shut-off element A5 and the check valve R2, while the shut-off element A2 is simultaneously closed.

[0033] In heating mode of the refrigerant circuit 11, the shut-off valve A4 is closed and the shut-off valve A3 is opened so that hot refrigerant can flow into the heating branch 16.1.

[0034] In order to carry out the heating function by means of the chiller 28 to implement water heat pump operation, the refrigerant compressed by the refrigerant compressor 12 flows via the open shut-off valve A3 into the heating register 26. At the heating register 26, heat is transferred to a supply air flow L led into the vehicle interior. The refrigerant then flows via the open shut-off valve A1 and the branch point Ab1. It is expanded by means of the expansion valve AE1 in the chiller 28 to absorb waste heat from the electrical and / or electronic components arranged in a coolant circuit 28.2. During this heating function, the expansion valves AE3 and AE4 are closed, the shut-off valve A5 is closed, and the shut-off valve A2 is open. In this case, refrigerant removed from a bidirectional branch 14.1 orsucked out of the primary line 14 and fed to the collector 24 via the check valve R2.

[0035] To perform the heating function using the external heat exchanger 18 as a heat pump evaporator, the refrigerant compressed by the refrigerant compressor 12 flows into the heating register 26 via the open shut-off valve A3 to release heat to a supply air flow L. It is then expanded via the open shut-off valve A1 by means of the expansion valve AE3 into the external heat exchanger 18 to absorb heat from the ambient air. The refrigerant then flows via a heat pump return branch 15 to the collector 24 and back to the refrigerant compressor 12. The expansion valves AE1, AE2, and AE4, as well as the shut-off valve A5, remain closed.

[0036] An indirect delta connection can be realized by expanding the refrigerant compressed by the refrigerant compressor 12 into the chiller 28 by means of the expansion valve AE1 when the shut-off valve A1 is open. At the same time, no mass flow is generated on the coolant side, i.e., in the coolant circuit 28.2. For example, the fluid used as coolant, such as water or a water-glycol mixture, remains on the coolant side of the chiller 28, or the chiller 28 is not actively flowed through by coolant. The expansion valves AE2, AE3, and AE4 remain closed in this switching variant.

[0037] During reheating or reheating operation, the supply air flow L supplied to the vehicle interior is first cooled and thus dehumidified by the evaporator 22. With the heat transferred to the refrigerant through evaporation and dehumidification, as well as the heat supplied to the refrigerant via the compressor 12, the supply air flow L can be completely or at least partially reheated by the heating register 26.

[0038] For this purpose, the refrigeration system 10, in particular the air conditioning unit 32, has adjustable, in particular controllable and pivotable, temperature flaps 34 between the evaporator 22 and the heating register 26. In the example shown, a left and a right temperature flap 34L and 34R (in Fig. 1 schematically shown). The temperature flaps 34L, 34R can be adjusted or pivoted between an open position, referred to as the 100% position, and a closed position, referred to as the 0% position. Alternatively, it is also possible to install the temperature flaps 34R, 34L downstream of the heating register 26.

[0039] In the 100% position, the entire supply air flow L passing through the evaporator 22 is guided over the heating register 26 and heated before it can flow into the passenger compartment of the vehicle. In the 0% position, the entire supply air flow L passing through the evaporator 22 flows in a bypass around the heating register 26 without being heated and thus without absorbing heat into the passenger compartment.

[0040] In an x-position of the temperature flaps 34L and 34R with 0% < x < 100%, these temperature flaps are only partially open, so that only a partial air flow of the supply air flow L flowing through the evaporator 22 is guided over the heating register 26. This heated partial air flow can then be mixed with the remaining, cooled and dehumidified partial air flow. The supply air flow L heated in this way is fed into the passenger compartment of the vehicle. For example, a 50% position indicates that the temperature flaps 34R and 34L are only half open, i.e., 50%.

[0041] The refrigeration system 10 has a sensor device 36 in the secondary branch 16 downstream of the secondary branch valve A3 and upstream of the heating register 26, which is configured to detect a hot gas temperature value representing the temperature of the gaseous refrigerant upstream of the heating register 26. The hot gas temperature value can be measured or detected directly or estimated indirectly based on other system parameters. For example, it is conceivable to use the sensor device 36 to determine a pressure in the secondary branch 16 and to draw conclusions about the hot gas temperature value from this. The sensor device 36 can, for example, be a pure temperature sensor or a combined temperature / pressure sensor.

[0042] The method proposed here can in principle be used in each of the operating modes described above, such as AC operation, heating operation, each with / without integration of heat pump function, whereby it is assumed that either the primary branch 14 or the secondary branch 16 is not actively flowed through by refrigerant, i.e. are inactive when the primary branch valve A4 is closed or the secondary branch valve A3 is closed.

[0043] From the Fig. 1 shows that the shut-off valve A2 is provided in the line section 15. The shut-off valve A2 is arranged on the high-pressure side of the primary line 14, with the line section 15 connecting the primary line 14 to the low-pressure side of the refrigerant circuit 11 upstream of the refrigerant compressor 12.

[0044] Furthermore, the shut-off valve A5 is provided in the line section 15a. The shut-off valve A5 is arranged on the high-pressure side of the secondary branch 16, with the line section 15a connecting the secondary branch 16 to the low-pressure side of the refrigerant circuit 11 upstream of the refrigerant compressor 12.

[0045] In order to determine the pressure in an inactive branch 14, 16 or area of the refrigerant circuit 11, respective sensor devices pT6 and pT7 are assigned to the primary branch 14 and the secondary branch 16. The sensor devices pT6, pT7 can be pressure sensors or pressure / temperature sensors. The respective pressure sensors pT6, pT7 are each arranged downstream of the primary branch valve A4 and the secondary branch valve A3, respectively. Thus, with respect to a typical refrigerant flow direction, they are located downstream of the respective shut-off device A3, A4, which is used to activate or deactivate the respective branch 14, 16.

[0046] The method 500, which can be carried out for the targeted extraction of refrigerant from inactive areas of the refrigeration system 10, is described below with reference to the Fig. 2 described in more detail.

[0047] According to the Fig.In the method 500 shown in Figure 2, after the start (S501) of the refrigeration system 10, the switching to a desired or suitable mode takes place during operation, which is illustrated by step S502. According to a step S503, the pressure p_inak is recorded in an inactive branch or region of the refrigeration system 10. In step S504, it is checked whether the recorded pressure value p_inak is less than the static pressure pR that occurs at ambient temperature. If the pressure p_inak in the relevant branch 14, 16 is less than the static pressure pR, the method is terminated, since no further extraction from the inactive branch 14, 16 is necessary or possible. If the detected pressure p_inak is greater than or equal to the resting pressure pR, it is checked according to step S505 whether the working pressure pA on the low-pressure side of the refrigerant circuit 11 is greater than the pressure p_inak detected in the inactive branch 14, 16.

[0048] If the working pressure pA is greater than the pressure p_inak, the working pressure pA is actively reduced to a value lower than the pressure p_inak according to step S506. For this purpose, the components of the relevant branch 14, 16 through which flow is actively carried out, in particular associated valve devices such as expansion valves AE1, AE2, AE3, but also the compressor 12, can be actively controlled such that a lower working pressure pA is temporarily established. If the working pressure pA is lower than the pressure p_inak, a check is carried out according to step S507 as to whether the working pressure pA is greater than a low-pressure limit p_grenz. If the working pressure pA is greater than the low-pressure limit p_grenz, the working pressure pA is actively reduced further (S506) or can be reduced further (S506).If the working pressure pA reaches the low-pressure limit p_limit, no further active reduction of the working pressure pA occurs, and the working pressure is regulated to a suitable value (S508) or maintained at the low-pressure limit p_limit, which is illustrated by the two arrows pointing upwards and downwards. Even if this is not explicitly shown in the method sequence, the method 500 naturally also includes, at an appropriate point, the opening of a relevant valve device, in particular the shut-off valve A2 or A5, in order to be able to establish the suction connection between the low-pressure side and the inactive branch 14 or 16.

[0049] The combination of the condition in S505 and step S506—that is, a targeted reduction in the working pressure pA, if this would actually be higher than the pressure p_inak in the inactive line during normal operation—can be described or understood as the first mode of active refrigerant recovery. The first mode therefore results in forced recovery because, during normal operation of the refrigeration system, it cannot be guaranteed that recovery would occur automatically due to the prevailing pressure conditions.

[0050] The combination of the condition in S507 and step S506, i.e., a further reduction in the working pressure pA, even if it is already below the pressure p_inak in the inactive branch, can be referred to or understood as a second mode of active refrigerant recovery. The second mode leads to accelerated refrigerant recovery.

[0051] The use of the method is explained below using some examples of different operating modes of the refrigeration system 10.

[0052] In pure AC operation (cooling the interior), the refrigerant actively flows in the primary line 14 from the refrigerant compressor 12 via the open primary line valve A4, the external heat exchanger 18, and the evaporator 22, with the secondary line valve A3 and valves A1, AE1, and AE4 closed. On the low-pressure side, i.e., downstream of the evaporator 22, a working pressure pA is then established, which is typically lower than the pressure p_inak detected in the inactive line 16 by the sensor pT6. Accordingly, in such pure AC operation, the second mode of active recovery is generally considered, whereby the already lower working pressure pA is further reduced in order to recover more refrigerant from the inactive line 16 via the open shut-off valve A5.

[0053] In heating mode with water heat pump function, the refrigerant actively flows in the secondary line 16 from the refrigerant compressor 12 via the open secondary line valve A3, the heat exchanger 26 (heating register) acting as a heat source, and the chiller 28 (water heat pump), with the primary line valve A4 and valves AE2, AE3, and AE4 closed. On the low-pressure side, i.e. downstream of the chiller 28, a working pressure pA is then established, which is not necessarily lower than the pressure p_inak detected in the inactive line 14 by the sensor pT7. Accordingly, in such heating mode with water heat pump function, the first mode of active extraction is generally considered, whereby the working pressure pA is actively reduced in order to extract refrigerant from the inactive line 14 via the open shut-off valve A2.

[0054] Active extraction of refrigerant from an inactive line or area or section of the refrigeration system 10 is also possible in other operating states of the refrigeration system 10, for example in the so-called reheating or reheat operation.

[0055] In principle, the method 500 presented here involves an active and at least temporary adjustment of the low pressure level (working pressure pA), which is or comes to be below the pressure level (pressure p_inak) in the inactive line or area.

[0056] Basically, it should be noted that the extraction of refrigerant and thus its transfer from an inactive branch or system section to an active one can only take place if the pressure level on the active system side is below the pressure level of the inactive system side and therefore the extraction prerequisite is: p_ab <p_inak

[0057] As already mentioned in the introduction, it should be noted again that the method 500 described above can be used for any type of refrigeration system that has a system with segmentable sections. The method can therefore be used both for a pure refrigeration system and for a system 10 described here as an example with a heat pump and / or reheat function, so that the associated advantages can be positively and specifically exploited. The simplest variant can be seen, for example, as a refrigeration system that has a second evaporator strand in the form of a chiller or air-charged evaporator, wherein the additional or second strand can be represented in a segmentable manner.

Claims

[1] Method (500) for operating a refrigeration system (10) for a motor vehicle, the refrigeration system (10) comprising: a refrigerant compressor (12) connected to a primary line (14) and connectable or connected to a secondary strand (16); a direct or indirect external heat exchanger (18) arranged in the primary line (14); an evaporator (22) arranged in the primary line (14); at least one further heat exchanger representing a heat source, in particular a heating register (26), which is arranged in the secondary branch (16); a primary branch valve (A4) arranged between the refrigerant compressor (12) and the external heat exchanger (18); a secondary branch valve (A3) arranged between the refrigerant compressor (12) and the further heat exchanger, in particular a heating register (26), representing a heat source; at least one valve device (A2, A5) arranged between a high-pressure side section (15, 15a) of the primary line (14) or the secondary line (16) and a low-pressure side line section located upstream of the refrigerant compressor (12), wherein the method (500) comprises the following steps: Setting (S502) an operating mode of the refrigeration system with active primary line (14) and inactive secondary line (16) or with active secondary line (16) and inactive primary line (14); characterized by Detecting (S503) the pressure (p_inak) in the inactive strand (14, 16); Activating a suction of refrigerant from the inactive branch (14, 16) into the active branch (14, 16) by lowering (S506) the pressure (pA) in the active branch (14, 16) to a value below the pressure (p_inak) in the inactive branch (14, 16) and by opening the relevant valve device (A2, A5). [2] Method (500) according to claim 1, wherein the pressure (pA) in the active strand (14, 16) is reduced (S505) starting from a working pressure level which is higher than the pressure in the inactive strand (14, 16). [3] Method (500) according to claim 1, wherein the pressure (pA) in the active strand (14, 16) is further reduced (S507) starting from a working pressure level which is lower than the pressure (p_inak) in the inactive strand (14, 16). [4] Method (500) according to claim 2 or 3, wherein the pressure (pA) in the active line (14, 16) is maintained (S509) at a pressure level which corresponds to a low pressure limit (p_grenz) permissible for the refrigeration system. [5] Method (500) according to one of the preceding claims, wherein the pressure value (p_inak) detected in the inactive branch (14, 16) is compared with the static pressure (pR) occurring at the prevailing ambient temperature or the prevailing coolant / fluid temperature, and wherein the activation of the suction of coolant from the inactive branch (14, 16) takes place when the detected pressure (p_inak) is greater than or equal to the static pressure (pR) occurring at the prevailing ambient temperature (S504). [6] Method (500) according to one of the preceding claims, wherein the activation of the suction of refrigerant from the inactive line (14, 16) occurs when starting the refrigeration system or when restarting the refrigeration system in order to maximize the amount of refrigerant in the active line (14, 16). [7] Refrigeration system (10) with heat pump function for a motor vehicle, the refrigeration system (10) comprising: a refrigerant compressor (12) connected to a primary line (14) and connectable or connected to a secondary strand (16); a direct or indirect external heat exchanger (18) arranged in the primary line (14); an evaporator (22) arranged in the primary line (14); at least one further heat exchanger representing a heat source, in particular a heating register (26), which is arranged in the secondary branch (16); a primary branch valve (A4) arranged between the refrigerant compressor (12) and the external heat exchanger (18); a secondary branch valve (A3) arranged between the refrigerant compressor (12) and the further heat exchanger, in particular a heating register (26), representing a heat source; at least one valve device (A2, A5) arranged between a high-pressure side section (15, 15a) of the primary line (14) or the secondary line (16) and a low-pressure side line section upstream of the refrigerant compressor (12), at least one pressure sensor (pT6, pt7) or pressure / temperature sensor arranged in the respective high-pressure side section (15, 15a) of the primary branch (14) or the secondary branch (16), characterized by that the pressure sensor (pT6, pt7) or pressure / temperature sensor is designed to, in an operating state with active primary line (14) and inactive secondary strand (16) or with active secondary strand (16) and inactive primary strand (14) to detect the pressure (p_inak) in the inactive strand (14, 16), and the refrigeration system (10) comprises a control device which is designed to carry out the method according to one of the preceding claims. [8] Motor vehicle, in particular at least partially electrically operated motor vehicle, with a refrigeration system (10) according to claim 7.

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