Method for operating a coolant circuit and vehicle air-conditioning system

1. A method for operating a coolant circuit of a vehicle cooling system in an AC mode and in a heating mode, implemented by a heat pump function, comprising:

an evaporator branch having an evaporator and an expansion element associated with the evaporator;

a coolant compressor;

an AC and heat pump branch having an outer condenser or gas cooler and a second expansion element as a heat pump evaporator for the heating mode, wherein the AC and heat pump branch is connected to the high pressure outlet of the coolant compressor via a first blocking element and to the evaporator branch via the second expansion element;

a heating branch having an inner heating condenser or heating gas cooler and a second blocking element connected downstream thereto, wherein the heating branch is connected to the high pressure outlet of the coolant compressor via a third blocking element and to the evaporator branch via the second blocking element;

a third expansion element with which the heating branch is connected to the AC and heat pump branch; and

a temperature measuring device for determining the coolant temperature at the inlet of the heating condenser or heating gas cooler, wherein

in the heating mode, the coolant temperature at the inlet of the inner heating condenser or heating gas cooler is limited to a maximum temperature value

wherein the following process steps are performed at a startup in AC mode:

extracting coolant from the heating branch by opening the second blocking element and closing both the third blocking element and the third expansion element; and

closing the second blocking element, either if coolant pressure downstream of the second blocking element rises or after a defined period of time.

2. The method according to claim 1 , wherein:

the temperature measuring device is disposed at the high pressure outlet of the coolant compressor; and

the coolant temperature at the inlet of the heating condenser or heating gas cooler is determined by a sensor value generated by the temperature measuring device.

3. The method according to claim 1 , wherein the coolant temperature is determined by a temperature measuring device disposed at the inlet of the heating condenser or heating gas cooler.

4. The method according to claim 1 , wherein the coolant pressure downstream of the second blocking element is detected indirectly in that the blower load of a blower of an air-conditioning device and/or the setpoint value of air temperature at the evaporator set by a controller of the coolant circuit and/or the pressure curve of the coolant on the low pressure side of the coolant circuit is/are detected and the second blocking element is closed if the blower load decreases and/or the setpoint value increases and/or the coolant pressure on the low pressure side increases.

5. The method according to claim 1 , wherein the coolant pressure downstream of the second blocking element is determined directly by a pressure sensor connected downstream thereof.

6. The method according to claim 1 , wherein the following process steps are performed at a startup in heating mode by a heat pump function or a triangular process:

providing a chiller branch having a chiller and an associated fourth expansion element to implement the heat pump function, wherein the chiller branch is connected in parallel to the evaporator branch;

extracting coolant from the AC and heat pump branch by opening a fourth blocking element, which connects the AC and heat pump branch to the low pressure side of the coolant circuit, and closing the third and the second expansion elements and the first blocking element; and

closing the fourth blocking element, either if coolant pressure downstream of the fourth blocking element rises or after a defined period of time.

7. The method according to claim 6 , wherein the coolant pressure downstream of the fourth blocking element is detected indirectly in that the coolant temperature of the chiller is detected and the fourth blocking element is closed when the coolant temperature rises.

8. The method according to claim 6 , wherein the coolant pressure downstream of the fourth blocking element is determined directly by a pressure sensor connected downstream thereof.

9. The method according to claim 1 , wherein the following process steps are performed at a startup in AC mode:

providing a check valve connected downstream of the second blocking element to prevent a return flow of coolant into the heating branch;

extracting coolant from the heating branch by opening the second blocking element and closing both the third blocking element and the third expansion element; and

expanding the coolant downstream of the second blocking element to low pressure level by the second expansion element while the first and/or fourth expansion elements are open to the maximum extent.

10. The method according to claim 1 , wherein the following process steps are performed at a startup in AC mode:

providing a heat pump return branch having a fourth blocking element and a check valve, wherein the AC and heat pump branch and the heat pump return branch are connected to the evaporator branch downstream of the evaporator;

providing an extraction branch having a fifth expansion element, wherein the extraction branch and the heat pump return branch are connected to the heating branch downstream of the inner heating condenser or heating gas cooler; and

extracting coolant from the heating branch by opening the fifth expansion element and closing the second, third, and fourth blocking elements and the third expansion element.

11. A vehicle cooling system having a coolant circuit for an AC mode and a heating mode, comprising:

an evaporator branch having an evaporator and an expansion element associated with the evaporator;

a coolant compressor;

an AC and heat pump branch having an outer condenser or gas cooler, and a second expansion element as a heat pump evaporator for the heating mode, wherein the AC and heat pump branch is connected to the high pressure outlet of the coolant compressor via a first blocking element and to the evaporator branch via the second expansion element;

a heating branch having an inner heating condenser or heating gas cooler and a second blocking element connected downstream thereto, wherein the heating branch can be connected to the high pressure outlet of the coolant compressor via a third blocking element and to the evaporator branch via the second blocking element;

a third expansion element with which the heating branch can be connected to the AC and heat pump branch; and

a temperature measuring device for determining the coolant temperature at the inlet of the heating condenser or heating gas cooler

wherein the following process steps are performed at a startup in AC mode:

extracting coolant from the heating branch by opening the second blocking element and closing both the third blocking element and the third expansion element; and

closing the second blocking element, either if coolant pressure downstream of the second blocking element rises or after a defined period of time.

12. The vehicle cooling system according to claim 11 , wherein a pressure sensor is connected downstream of the second blocking element.

13. The vehicle cooling system according to claim 11 , wherein

a chiller branch having a chiller and an associated fourth expansion element is provided for implementing a water heat pump function;

the chiller branch is connected in parallel to the evaporator branch; and

a fourth blocking element is provided, with which the AC and heat pump branch is connected to the low pressure side of the coolant circuit, and

a pressure sensor is provided downstream of the fourth blocking element.

14. The vehicle cooling system according to claim 11 , wherein a check valve is connected downstream of the second blocking element.

15. The vehicle cooling system according to claim 11 , wherein

a heat pump return branch having a fourth blocking element and a check valve is provided, wherein the AC and heat pump branch and the heat pump return branch can be connected to the evaporator branch downstream of the evaporator; and

an extraction branch having a fifth expansion element is provided, wherein the extraction branch and the heat pump return branch can be connected to the heating branch downstream of the inner heating condenser or heating gas cooler.