Checking compressed-air system of spring-loaded parking brake

AR42.20-L-0580B

Checking compressed-air system of spring-loaded parking brake

21.11.03



Check

1

Fill out data sheet for spring brake compressed-air system

 Enclose measured values with the order. Data sheet; Check compressed-air system of spring brake, form: 

Data sheet for vehicles as of VIN 101651

OF42.20-L-3000-01B

2

Bleed spring-loaded parking brake system

3

Connect pressure gauge of test kit to test connection (H1)

 Between non-return valve (F) and compressed air reservoir V1 (C2).

 Test kit

*360589002100

4

Connect pressure gauge of test kit to test connection (H2)

 After overflow valve (D3).

 Test kit

*360589002100

5

Check cut-out pressure of pressure switch II (spring actuator) B14 (E3)

 Pressurize spring-loaded parking
brake system. Check pressure at test connection (H1) when standby lamp "(!)"
is extinguished and compare with
specified value.

*BE42.20-N-1007-01C

If the cut-out pressure of pressure switch II (spring actuator) B14 (E3) (color coding yellow) deviates from the specified value: 

Replace pressure switch II (spring actuator) B14 (E3) (color coding yellow).

 Test kit

*360589002100

6

Check cut-in pressure of pressure switch I (spring actuator) B13 (E6)

Bleed spring actuator parking brake system until the readiness lamp "(!)" lights up.

Check pressure at test connection (H1) when standby lamp "(!)" comes on and compare with specified value.

*BE42.20-N-1006-01C

If the cut-in pressure of pressure switch I (spring actuator) B13 (E6) (color coding red) deviates from the specified value :



Replace pressure switch I (spring actuator) B13 (E6) (color coding red).

 Test kit

*360589002100

7

Check pressure switch for reservoir pressure B12 (E1) on compressed air reservoir V2 (C1)

 The "compressed air reservoir" lamp is located on the right-hand side of the instrument cluster.

*BE42.20-N-1008-01C

Pressurize spring-loaded parking brake system. Check pressure at test connection (H2) when brake-air pressure lamp is extinguished and compare with
specified value.

If the switching point of the pressure switch for reservoir pressure B12 (E1) (yellow indicator lamp) deviates from the specified value: 

Replace pressure switch for reservoir pressureB12 (E1) (yellow indicator lamp).

 Test kit

*360589002100

8

Check opening pressure of
overflow valve (2)

 Check pressure at test connection (H2) and compare with specified value.

If release pressure differs from specified value:

*BE42.20-N-1012-01C

Adjust overflow valve (2).

If the specified value is not reached, replace overflow valve (2).

 Test kit

*360589002100

9

Connect test kit pressure gauge to test connection (H3) in the area of the spring-loaded cylinder (G1)

 Test kit

*360589002100

10

Check cut-in/cut-out pressure of parking brake pressure switch B5 (E5)

 Pressurize spring-loaded parking
brake system. Check pressure at test connection (H3) when the parking lamp "P" goes out and compare with specified value. If the switching point of the parking brake pressure switch B5 (E5) deviates from the specified value: 

*BE42.20-N-1009-01C

Replace parking brake pressure
switch B5 (E5).

 Test kit

*360589002100

11

Check cut-in and cutout points of electric compressor (A)

 Check cutoff pressure of pressure governor to determine cut-in and cutout point of electric compressor (A).

AR42.20-L-0002B

12

Bridge pin 5 and pin 1 at relay K18

 Use a fuse for the bridge as defects at other electrical components may occur due to a short circuit.

 The compressor operates continuously once the ignition is turned on.

13

Check opening pressure of safety valve (D2) at test connection (H1)

 The compressor must be in continuous operation during the test, although it may turn off internally depending on the temperature. If the opening pressure of the safety valve (D2) deviates from the specified value: 

*BE42.20-N-1013-01C

Replace safety valve (D2).

 Test kit

*360589002100

14

Check drain valve of air drier (B)

 Switch on ignition and wait until the compressor switches off.

*BE42.20-N-1011-01C

 Once the compressor switches off the drain valve opens (hisses audibly).

If the drain valve does not open: 

Check electrical connection on drain valve.

If the electrical connection on the drain valve is OK: 

Replace air drier (B).

15

Disconnect pressure gauge of test kit from test connection (H1)

 Between non-return valve (F) and compressed air reservoir V1 (C2).

 Test kit

*360589002100

16

Disconnect pressure gauge of test kit from test connection (H2)

 After overflow valve (D3).

 Test kit

*360589002100

17

Disconnect pressure gauge of test kit from test connection (H3)

 Near spring brake cylinder (G1).

 Test kit

*360589002100

Number

Designation

Models
668, 670
as of VIN 101651 except code B16, except
670.398/4

BE42.20-N-1003-01C

Pressure loss of parking braking system at 3 bar
over 60 seconds

%

5

BE42.20-N-1006-01C

Activation pressure standby indicator lamp "(!)" Pressure switch B13

bar

5.5 (0,2)

BE42.20-N-1007-01C

Cut-off pressure standby indicator lamp "(!)"
Pressure switch B14

bar

8.4 (0,4)

BE42.20-N-1008-01C

Cut-in/cutoff pressure for compressed-air tank pressure indicator lamp V2, pressure switch B12

bar

5.8 (0,3)

BE42.20-N-1009-01C

Cut-in/cutoff pressure for parking brake malfunction indicator lamp "(P)", pressure switch B5

bar

5.8 (0,3)

BE42.20-N-1011-01C

Cutoff pressure of electric air compressor, pressure switch B74

bar

12 (-0.5)

BE42.20-N-1012-01C

Release pressure of overflow valve

bar

10.5 (-0.3)

BE42.20-N-1013-01C

Opening pressure of safety valve

bar

13.8 (+1.2)

BE42.20-N-1014-01C

Opening time of air drier purge valve

s

10