Check compressed air system · sm4220l0007a · Mercedes-Benz WIS

SM42.20-L-0007A

Check compressed air system

18.2.99

MODELS 668.###, 670.### ## up to 070980
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

N42.20-2026-01

Figure 1

P1 Test connector

Fig. 2

P2 Test connector

1 Adjustment screw

2 Overflow valve

N42.20-2033-01

N42.20-2034-01

Fig. 3

V2 Boiler 2

B12 Switch

Figure 4

P3 Test connector

N42.20-2035-01

N42.20-2041-01

Figure 5

B13 Switch

B14 Switch

B74 Switch

B75 Switch

Modification notes

19.1.00

Operation 13 added in accordance with STIN 43.04L002 of 5.11.99

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 "!")	 Measure pressure at test connection P1 Switch on using switch B13 when pressure drops below 5.8 bar  0.3 bar. Switch off using switch B14 when pressure rises above 8.4 bar  0.4 bar
2	Pressure supply lamp at boiler V2 (Figures 2 and 3)	 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 4)	 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).
		 When carrying out conversions in the winter months, ensure that any condensation that is present is drained off: 
11	Operate drain valves several times and also pour approx. 5 ccm of antifreeze (Wabcothyl) into the pressure circuit downstream of the air dryer	 The antifreeze must not be poured in upstream of the air dryer, since this may destroy the air dryer.