Expansion Valve With And Without Shut-Off Valve
Expansion Valve without Shut-Off Function
The expansion valve -A- atomizes the streaming refrigerant and controls the flow rate so that the vapor is gaseous only at the evaporator outlet, depending on the heat transmission.
With the introduction of the refrigerant R1234yf, the expansion valves were adapted to the refrigerant (different ; characteristic curves), therefore, make sure the correct version is used. Refer to the Parts Information.
Different versions of the expansion valve due to different characteristic curves that must be adapted to the refrigerant circuit. Refer to Refrigerant Circuit (vehicle-specific Service Information) and the Parts Information.
Be sure to use the correct part number when replacing the expansion valve. Refer to the Parts Information
Depending on the A/C compressor version, there may be a valve installed on the high pressure side of the A/C compressor, which prevents the liquid refrigerant from flowing back into the A/C compressor once the A/C system is turned off. If an A/C compressor with this valve is installed in a vehicle with a refrigerant circuit having an expansion valve, then it may take some time until the pressure in the high pressure side decreases (the expansion valve is cold and the pressure in the low pressure side quickly increases after it is turned off, the expansion valve closes and the refrigerant can flow slowly to the low pressure side). If the A/C compressor is switched on, the pressure on the low pressure side decreases, the expansion valve opens and the refrigerant can flow to the low pressure side.
Expansion Valve with Refrigerant Shut-Off Valve
There are different versions of the shut-off valve with different functions and with different names. Refer to Refrigerant Circuit (vehicle-specific Service Information).
- The expansion valve -A- with shut-off valve -B- atomizes the streaming refrigerant and regulates the refrigerant flow rate to the evaporator in the battery cooling module for the Hybrid Battery Unit -- so that the vapor becomes gaseous only at the evaporator output, depending on the heat transmission.
- If the shut-off -B- is activated by the electronics, it is open and lets the refrigerant flow through to the expansion valve -A-.
- If the shut-off valve -B- is open and the expansion valve -A- lets the refrigerant flow according to its control characteristic to the evaporator or the heat exchanger. Refer to Refrigerant Circuit (vehicle-specific Service Information).
- The solenoid coil -B- on the expansion valve -A- is activated by different control modules depending on the vehicle. Refer to Wiring Diagram and Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
- If, for a vehicle with two evaporators (one in the heater and A/C unit and one in the battery cooling module, for example on the Q5 Hybrid), the measured temperature on one of the evaporators corresponds to the specified value or the specified value falls short, but does not reach the required specified value on the other evaporator, the following adjustment is performed: the corresponding control module (Battery Regulation Control Module -J840-) activates the electric A/C compressor with increased speed (thereby increasing the A/C system cooling output and decreasing the pressure on the low pressure side as well as the evaporator temperature) via (for example the Electric Drive Power and Control Electronics -JX1-) and the A/C Compressor Control Module -J842-. If then the specified value for the temperature on the value falls below, the respective control module activates the corresponding shut-off valve (for example, the Battery Regulation Control Module Battery Regulation Control Module -J840-, the Hybrid Battery Refrigerant Shut-Off Valve 1 -N516- or the Hybrid Battery Refrigerant Shut-Off Valve 2 -N517-) so that no more refrigerant flows through the evaporator which is too cold. Refer to Refrigerant Circuit (vehicle-specific Service Information) and Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.