Modular cooling system for a vehicle with a plurality of modules for performing different functions: a) a base module for performing a cooling function, having a1) a refrigerant compressor (2.1), a2) a high-pressure section (2.2) connectable to the high-pressure outlet of the refrigerant compressor (2.1) by means of a shut-off element having a direct or indirect condenser or gas cooler (2.3), wherein the direct or indirect condenser or gas cooler (2.3) can be operated in a cooling system operation and in a heat pump operation, and a3) a low-pressure section (2.4) connected to the low-pressure inlet of the refrigerant compressor (2.1) with at least one evaporator (2.5) and a chiller (2.6) with chiller extension elements connected upstream, wherein the low-pressure section (2.4) is connected upstream to the high-pressure section (2.2) via a heat pump extension element, b) a first extension module for performing a heating and reheating function, having b1) a heating branch (3.1) connectable to the high-pressure outlet of the refrigerant compressor (2.1) by means of a shut-off element with a heat pump heat exchanger (3.2), which can be connected to the direct or indirect condenser or gas cooler (2.3) via a first reheating branch (3.3) with a blockable valve element, and b2) a heat pump return branch (3.4) with a blockable valve element for connecting the direct or indirect condenser or gas cooler (2.3) to the low-pressure section (2.4), characterised by the combination with c) a second extension module for performing an air-preheating function by means of the evaporator (2.5), having c1) a preheating branch (4.1) with a preheating extension element, wherein the preheating branch (4.1) connects an outlet (3.20) of the heat pump heat exchanger (3.2) to an outlet (2.50) of the evaporator (2.5), wherein the outlet (2.50) of the evaporator (2.5) is related to its cooling operation, and c2) a blockable valve element, by which the low-pressure section (2.4) of the base module is connected to the outlet (2.50) of the evaporator (2.5), wherein - to reduce the number of functions the first extension module or the second extension module can be omitted, or - the first extension module and the second extension module can be omitted for providing a basic cooling system. a) a base module for performing a cooling function, having a1) a refrigerant compressor (2.1), a2) a high-pressure section (2.2) connectable to the high-pressure outlet of the refrigerant compressor (2.1) by means of a shut-off element having a direct or indirect condenser or gas cooler (2.3), wherein the direct or indirect condenser or gas cooler (2.3) can be operated in a cooling system operation and in a heat pump operation, and a3) a low-pressure section (2.4) connected to the low-pressure inlet of the refrigerant compressor (2.1) with at least one evaporator (2.5) and a chiller (2.6) with chiller extension elements connected upstream, wherein the low-pressure section (2.4) is connected upstream to the high-pressure section (2.2) via a heat pump extension element, b) a first extension module for performing a heating and reheating function, having b1) a heating branch (3.1) connectable to the high-pressure outlet of the refrigerant compressor (2.1) by means of a shut-off element with a heat pump heat exchanger (3.2), which can be connected to the direct or indirect condenser or gas cooler (2.3) via a first reheating branch (3.3) with a blockable valve element, and b2) a heat pump return branch (3.4) with a blockable valve element for connecting the direct or indirect condenser or gas cooler (2.3) to the low-pressure section (2.4), characterised by the combination with c) a second extension module for performing an air-preheating function by means of the evaporator (2.5), having c1) a preheating branch (4.1) with a preheating extension element, wherein the preheating branch (4.1) connects an outlet (3.20) of the heat pump heat exchanger (3.2) to an outlet (2.50) of the evaporator (2.5), wherein the outlet (2.50) of the evaporator (2.5) is related to its cooling operation, and c2) a blockable valve element, by which the low-pressure section (2.4) of the base module is connected to the outlet (2.50) of the evaporator (2.5), wherein - to reduce the number of functions the first extension module or the second extension module can be omitted, or - the first extension module and the second extension module can be omitted for providing a basic cooling system. - to reduce the number of functions the first extension module or the second extension module can be omitted, or - the first extension module and the second extension module can be omitted for providing a basic cooling system.