G. Preglow System With Key Start System (Model 123.1)
Operation of Preglow SystemG. Preglow system with key start system engine 615,616,617 in model 123.1
Operation
When the steering lock starter switch is actuated in position ~ (preglowing, start) the preglow system is switched on by the preglow time relay. The extinguished preglow indicator lamp in instrument cluster shows that the engine is ready for starting. The glow plugs are started in series and protected with a 50 amps fuse.
The preglow current of approx. 50-55 amps is determined by the firm resistors of the glow plugs and the resistance conductors.
Too high a preglowing current is the result of a ground connection or short-circuit in preglow system, e.g. a defective glow plug.
Too low a preglowing current is the result of transition resistance caused e.g. by a loose glow plug connection or by an insufficiently charged battery.
The preglow time relay is attached to instrument cluster on pedal assembly.
The preglow time relay has an integrated power relay (a) for preglow current, a control relay (b) for switching off power relay, an electronic component (c) for the safety circuit and an electronic component (d) with a primary reed contact for the preglow indicator lamp.
In key position "2" terminal 4 of preglow time relay (1) is contacted via terminal 15 of steering lock starter switch (3) and the winding of power relay via the rest contact of control relay (b).
The contacts of the power relay are closing the preglow circuit. From B+ the preglow current flows across terminal 5 and 6 of preglow time relay (1) via fuse (8) and the glow plugs to ground.
Wiring Diagram (615, 616):
For preglowing, the preglow indicator lamp is switched by means of an electronic component in preglow time relay A temperature sensor (NTC) in coolant circuit changes its resistance (cold = high, warm = low resistance) in dependence of coolant temperature and activates the electronic component. After attaining the required preglow time, the preglow indicator lamp is switched off.
The optimal preglow period is indicated when the preglow indicator lamp goes out
Wiring Diagram (617):
In starting position the preglow time relay is contacted by terminal 50 of the steering lock starter switch via terminal 3. Control relay (b) is energized. The contacts are closing (interrupting the rest position) and remain closed via terminal 4 in a self-holding circuit.
The power relay (a) is not switching off, since during the starting operation the power relay is directly contacted via terminal 3. The preglow system remains switched on.
At end of starting operation the key moves back into position "2" (preglowing drive). The power relay switches off, since there is no voltage neither via terminal 3, nor via the interrupted rest contact of the control relay (b) which remains switched on via terminal 4. The preglow system is now in disconnected condition.
Attention!
If the engine is not started when the preglow mdicator lamp is extinguished, the preglow system remains switched on up to 90 + 20 seconds of preglow time.
When working in engine compartment, note that in such a case the resistance conductors are red hot.
After 90 + 20 seconds the safety relay is energized for a short moment by control relay (b). The control relay attracts and remains switched on under self-holding condition. The rest contact is interrupted and disconnects the voltage at power relay (a). As a result, the contacts of the power relay will interrupt the preglow current. The preglow system is now inoperative.