A.General Information

Since MY 1984, a new version orthopedic seat backrest (Multi-chamber system) is available as optional equipment on models 126 and 201.

This orthopedic backrest is available for both front seats in model 126, and the driver's seat in model 201 (armrest would interfere with the regulating valve on a passenger seat installation).

FIGURE 3:

The backrest contains six air cushions (5 cushions with leather seats, Figure 3), which are inflated individually (maximum 200 mbar) from the supply pump of the central locking system.. The desired cushion firmness and position in the backrest can be adjusted with the pressure and height selector (a and b, Figures 1 & 2) on the regulating valve. This setting will stay constant until the ignition is switched off, and is re-established after it is switched on again.
B. Description of Operation

The system is made up of the center air cushion consisting of three separate chambers (1-3, Figure 3), two side air cushions (4 and 5) and one small top cushion (6). The small air cushion (6) is omitted with leather seats.
1 Center air cushion chambers
2 Center air cushion chambers
3 Center air cushion chambers
4 Right side cushion
5 Left side cushion
6 Small top cushion
(omitted with leather seats)
7 Regulating valve
a Pressure selector b Height selector
8 Test plug
9 Filter
10 Supply pump c Unlocking circuit - to driver's door d Locking circuit - control actuator (central locking system) e Model 201 - To fuse no. 10, circuit 15 via terminal A/B of connector (C205 in ETM) behind driver's kickpanel e Model 126 - To fuse no. 9, circuit 15R f To central locking (pressure/vacuum)
11 Air pressure reservoir
M1 Main ground connection (behind instrument cluster)
Selectable height positions

Position Pressure in air cushions
(Lever b) 1 2 3 4-5(6)
A X X
B X X X
C X X
D X X X
E X X
1. Backrest Firmness Adjustment

Adjust the desired firmness in the air cushions with pressure selector "a" (variable from 0-4). Turn adjusting wheel forward until the desired setting of the backrest is obtained. This is accomplished by inflating air cushions 4-5(6), and depending on the height adjustment selection, one or two of chambers 1-3. To reduce the amount of firmness, turn the selector rearward, which allows air to vent via the regulating valve.

The selected pressure is sustained as long as the ignition is switched on. A slow air leak will be compensated for by the supply pump. With ignition off, the last cushion setting is retained in memory, and automatically adjusts the cushion to this setting after startup.

Air chambers 1-3 can be inflated in five stages (A-E) via the height selector "b". Depending on height adjustment, chambers 1-3 can be inflated individually (position A, C or E) or chambers 1 and 2, or 2 and 3 together (position B or D). Refer also to "selectable height positions" chart.

FIGURE 4 - MODEL 126 11 RESERVOIR:

FIGURE 5 - MODEL 201 11 RESERVOIR:

2. Air Supply to Cushions

Compressed air is delivered from the new version supply pump of the central locking system, which has an additional hose and electrical connection.

After the ignition is switched on the pump delivers up to approximately 500 mbar to the reservoir (11, Figure 4 & 5) and' through the regulating valve up to approximately 200 mbar (7, Figure 3) to the air cushions.
At an approximate pressure of 500 mbar, the supply pump switches off and comes on again when the pressure drops below 200 mbar, keeping approximately 200-500 mbar supplied to the regulating valve (7).
When inflating the cushions, the pump keeps running to its cut-out point of approximately 500 mbar. After it shuts off, it comes on again for a short while. These on/off cycles may repeat five times until the cushion air pressure is stabilized depending on the pressure adjustment "a". Although the pump compensates for slow leaks, it will shut off after running continuously for 70 seconds, in case of a major leak. If the pump keeps cycling in short intervals -(below 17 +/- 2 seconds), a leakage monitoring system adds up these cycles and will shut the pump off after a total of 31 cycles. This process is cancelled when the ignition system is turned off and starts from the beginning. The summation of on/off cycles is also cancelled when one off cycle is more than 17 +/- 2 seconds.

If the orthopedic backrest system and central locking system need pump action simultaneously, the central locking system has priority.

In the event that the pump is shut down after 70 seconds or 31 on/off cycles due to a leaking orthopedic backrest system, the function of the central locking system is not affected.