Check compressed air system · sm4220l0007b · Mercedes-Benz WIS

SM42.20-L-0007B

Check compressed air system

18.2.99

MODELS 668.###, 670.### ## as of 070981 up to 30.11.98
except CODE (B16) 2-circuit hydraulic brake/2-circuit compressed air brake
except CODE (B19) Hydraulic 2-circuit / compressed air 2-circuit heavy-duty brakes

N42.20-2028-01

Figure 1

V1 Boiler

P1 Test connector

B13 Switch, red

B14 Switch, yellow

B74 Switch, blue

B75 Switch, without

identification

Fig. 2

N42.20-2022-01

N42.20-2033-01

Fig. 3

P2 Test connector

1 Adjustment screw

2 Overflow valve

V2 Boiler

B12 Switch

Fig. 4

N42.20-2034-01

N42.20-2035-01

Figure 5

P3 Test connector

Figure 6

N42.20-2026-01

Operation no. of operation texts or standard texts and flat rates

Range	Op. no.	Operation text
N	023721	CHECKING OPERATION AND TIGHTNESS OF COMPRESSED AIR SYSTEM (AFTER WORKING ON THE SYSTEM) 8 WU/0.7 hrs.

	Testing
1	Check readiness lamp (brake lining wear indicator "!") (figures 1 and 2)	 Measure pressure at test connection P1 Switch on using switch B13 when pressure drops below 5.5 bar  0.3 bar. Switch off using switch B14 when pressure rises above 8.4 bar  0.4 bar
2	Supply pressure lamp ("Boiler" lamp, right side of instrument cluster) at boiler V2 (figures 3 and 4)	 Measure pressure at test connection P2 Switch B12, on/off switching point 5.8 bar  0.3 bar
3	Depressurize system
5	Attach 2 pressure gauges to test connections P1 and P2
6	Measure overflow valve setting	 Measure pressure at which overflow valve opens and fills boiler V2. Specified value 9.6 bar - 0.3 bar
7.1	Make overflow valve setting by adjusting screw	 Only if there is a difference
8	Check parking lamp "P" (figure 5)	 Measure with handbrake off, test connection P3. Switch B5, on/off switching point 5.8 bar  0.3 bar
9	Check compressor on/off switching points	 Read off pressure at test connection P1 Switch B75, compressor switch-on point 10.5 bar  0.5 bar Switch B74, compressor switch-off point 12.0 bar  0.5 bar


10	Check compressed air dryer drain valve	 After the ignition is switched on and the compressor switched off, the drain valve opens for approx. 4 sec. (audible hissing noise).