Manually release pressure in fuel cell system

AR06.00-P-1000RFW

Manually release pressure in fuel cell system

12.08.2019

Engine

780 in model 253.992/993

S7

High-voltage disconnect device

Vehicle in the lifted and secured state

MV

Manual valve

1

Electrical connector

B72/18

Mean pressure sensor

2

Plug

4

Electrical connector

Y94/7

Pressure regulating valve 1

 Danger

Risk of explosion caused by escaping hydrogen or overheating of the fuel tanks when working on the hydrogen system. Risk of frostbite to body parts caused by escaping gas and by touching component parts carrying gas when emptying fuel tanks. Risk of asphyxiation caused by inhalation of air diluted by hydrogen. Risk of burn injuries by coming into contact with an invisible pale blue hydrogen flame.

AS00.00-Z-0030-01B

Topical note

Information on preventing damage to electronic components due to electrostatic discharge

AH54.00-P-0001-01A

Topical note

Notes on fuel cell system

AH00.00-P-0022-01RFW

Notes on safety-relevant components

AH00.00-Z-0019-01A

Preparatory tasks

1

Print out the "Manual depressurization event log" form and fill it out during pressure reduction.



OF00.00-P-3000-22RFW

2

Park vehicle in the open air in the hydrogen discharge area.

3

Perform quick test for leaks.

AR06.00-P-0003RFW

If the measured hydrogen concentration is   8000 ppm or there is an audible leak in the fuel cell system,



Prepare vehicle with major leakage in fuel system for repair

AR47.60-P-0018RFW

4

Activate high-voltage disconnect device (S7), as shown in picture sequence (A, B, C), and lock it with a shackle-type lock.

Vehicle is accident-free, but no control unit communication with the fuel tank control unit (N3/19) is possible.

 For the electrical interruption of the tank components.

 Keep the key for the shackle-type lock of the high-voltage disconnect device (S7) in a separate location accessible to authorized personnel only.

5

Perform a diagnosis-based deactivation of the fuel cell in the powertrain control unit (N127).

Vehicle is accident-free, fault memory can be read out, but there are faulty components in the hydrogen system or a leak that cannot be localized has arisen.



AD00.00-P-2000-04B

 To do this, select the following menu item:
Powertrain control unit (N127) 
Actuations 
Status of the start approval for the fuel cell system component.

6

Perform a diagnosis-based deactivation of vehicle standby mode in the powertrain control unit (N127).

Vehicle is accident-free, fault memory can be read out, but there are faulty components in the hydrogen system or a leak that cannot be localized has arisen.



AD00.00-P-2000-04B

 To do this, select the following menu item:
Powertrain control unit (N127) 
Actuations 
Status of the start approval for the powertrain control unit component (N127).

7

Raise and secure the vehicle at the front with a commercially available vehicle jack or a hydraulic wheel gripper.

 Electrical tools are not permitted (explosion protection).

8

In exterior area, remove left center and transmission tunnel underfloor panelings.

AR61.30-P-1001RFW

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

9

Seal manual valves (MV) on both fuel tanks.

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

 The manual valves (MV) can be reached without removing the underfloor paneling.
The manual valves (MV) have a hexagon head with a wrench size of 7 mm.

 Torque for sealing of manual valve in valve unit

*BA47.60-P-1029-01B

Manual pressure reduction of the hydrogen high-pressure system to   1 bar

10

Wear personal protective equipment safety glasses and protective gloves.

 Personal protective equipment must always be worn when performing the following operation steps.

11

Cover the high-pressure line beside the medium pressure sensor (B72/18) with a suitable rag.


The rag serves to prevent confusion so that the high-pressure line is not released inadvertently.
The high-pressure line is subject to up to 700 bar (hydrogen).

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

12

Disconnect electrical connector (1).

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

13

Slowly unscrew the medium pressure sensor (B72/18) two revolutions and wait until pressure reduction has been audibly completed.

AR47.60-P-0014RFW

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

 The medium pressure sensor (B72/18) is subject to approx. 14 bar pressure (hydrogen).
The pressure is reduced via the thread of the medium pressure sensor (B72/18).
Do not use any electrical tools.

14

Check the hydrogen tank in the area around the medium pressure sensor (B72/18).



000 588 03 21 00 Gas detector

WS47.00-P-0019B

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

 specified value under 100 ppm.

15

Remove the medium pressure sensor (B72/18), check the sealing rings and then re-install them.

AR47.60-P-0014RFW

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

 Ensure scrupulous cleanliness.

If complaints are present,



replace the sealing ring or medium pressure sensor (B72/18).

Manual pressure reduction of the hydrogen medium-pressure system to   1 bar

16

Wear personal protective equipment safety glasses and protective gloves.

 Personal protective equipment must always be worn when performing the following operation steps.

17

Slowly loosen the stop plug (2) and wait until pressure reduction has been audibly completed.

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

 Electrical tools are not permitted (explosion protection).

 The stop plug (2) is subject to approx. 14 bar pressure (hydrogen).
The pressure is reduced via the thread of the stop plug (2).

 Ensure cleanliness. No chippings, friction or dirt must enter the fuel cell aggregate.

18

Check the hydrogen content in the area around the stop plug (2).



000 588 03 21 00 Gas detector

WS47.00-P-0019B

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

 specified value under 100 ppm.

19

Unscrew the stop plug (2) completely.

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

 Store the stop plug (2) in a clean, safe location.

Manual pressure release of fuel cell to below 1 bar

20

Wear personal protective equipment safety glasses and protective gloves.

 Personal protective equipment must always be worn when performing the following operation steps.

21

Disconnect the electrical connector (4) from the pressure regulating valve 1 (Y94/7).

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

22

Connect the power supply unit of the filling device to the pressure regulating valve 1 (Y94/7).



000 588 11 82 00 Filling unit

WS06.00-P-0028C

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

23

Switch on the power supply unit of the filling device and, for 60 s, activate the pressure regulating valve 1 (Y94/7).



000 588 11 82 00 Filling unit

WS06.00-P-0028C

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

 Switching on the power supply units causes the pressure regulating valve 1 (Y94/7) to open and pressure reduction to start.

 When pressure reductions starts, approx. 4 bar pressure (hydrogen) is applied to the pressure regulating valve 1 (Y94/7).
Pressure reduction is performed via the still open threaded hole of the stop plug.

24

Disconnect the power supply unit of the filling device from the electrical connector (4) on the pressure regulating valve 1 (Y94/7).



000 588 11 82 00 Filling unit

WS06.00-P-0028C

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

25

Connect the electrical connector (4) to the pressure regulating valve 1 (Y94/7).

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

26

Check the hydrogen content in the area around the threaded hole of the stop plug (2).



000 588 03 21 00 Gas detector

WS47.00-P-0019B

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

 specified value under 100 ppm.

27

Carefully clean the stop plug (2) and the thread of the pressure regulating valve 1 (94/7).

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

 Ensure cleanliness. No chippings, friction or dirt must enter the fuel cell aggregate.

 Installation: Check O-rings (3) for damage.

If damage is present,



replace the stop plug (2).

28

Screw in the stop plug (2).

 Commercially available devices/tools explosion-proof flashlight, comparable with AccuLux flashlight MHL 5 EX of the company Witte + Sutor GmbH.

 Stop plug to pressure regulating valve holder

*BA47.60-P-1032-01B

29

Inform the market support people in charge immediately as the fuel system will have to be discharged manually.

If one or both fuel tanks have to be removed for the following jobs.

Concluding tasks

30

Park vehicle on the wheels.

31

Remove U-shackle lock and connect high-voltage disconnect device (S7), as shown in picture sequence (D, E, F).

If the high-voltage disconnect device (S7) has been disconnected,

 Installation: Check high-voltage disconnect device (S7) for damage.

If damage is present,



Remove contacts from coupling housing of high-voltage disconnect device (S7) and replace high-voltage disconnect device (S7).

Remove/install contacts from coupling housing of high-voltage disconnect device.

AR00.19-P-0120-31A

 New passenger car wiring harness repair kit

*220589049900

 Unlocker with ejector MLK 1.2_plug

*220589019925

 Wiring harness repair kit, basic

*000589139900

32

Localize leakage on fuel cell system.

If damage-causing components or a hydrogen leak is present and cannot be localized.

AR06.00-P-0005RFW

33

Perform a diagnosis-based activation of vehicle standby mode in the powertrain control unit (N127) and drive the vehicle into the workshop with battery power.

Vehicle is accident-free, fault memory can be read out, but there are faulty components in the hydrogen system.



AD00.00-P-2000-04B

 To do this, select the following menu item:
Powertrain control unit (N127) 
Actuations 
Status of the start approval for the powertrain control unit component (N127).

34

Slide the vehicle into the workshop.

Vehicle has been in an accident and the airbag or pyrofuses have triggered, or vehicle is accident-free, but no control unit communication with the fuel tank control unit (N3/19) is possible.

 Use a commercially available hydraulic garage jack to lift and maneuver the vehicle.
Aid of helpers is required.
Deactivating the vehicle standby mode makes it impossible to release the parking brake.

35

Fill out the "Manual depressurization event log, form", sign it and attach it to the vehicle in a clearly visible location.



OF00.00-P-3000-22RFW

 Tank system

Number

Designation

Engine 780 in model 253.992/993
with code ME02 (Fuel cell)

BA47.60-P-1029-01B

Torque for sealing of manual valve in valve unit

Nm

6

 Tank system

Number

Designation

Engine 780 in model 253.992/993
with code ME02 (Fuel cell)

BA47.60-P-1032-01B

Stop plug to pressure regulating valve holder

Nm

40