F. Preglow System With Key Start System (Model 115.1)
Operation of Preglow SystemF. Preglow system with key start system engine 617 in model 115.1
Operation
When the steering lock starter switch is actuated, in position "2" (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.
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 pedal assembly behind instrument cluster.
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 a reed contact (d) as overload protection.
In key position "2" terminal 4 of preglow time relay (1) is contacted via terminal 15 of steering lock starter switch (4) and the winding of power relay (a) 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 via terminals Sand 6 of preglow time relay (1) across the glow plugs and the thermo time switch (6) to ground. The preglow system is in operation.
The preglow time is indicated by the preglow indicator lamp.
In dependence of the coolant temperature and the preglow current flowing across the thermo time switch, the pr°.glow indicator lamp is contacted with minus by the closed contact in thermo time switch. In parallel with the glow plugs, the control lamp is connected to plus by a line connected to the glow plug of the 5th cylinder. When the optimal preglow time is obtained, the contact in thermo time switch will interrupt minus and the preglow indicator lamp is extinguished. The engine is now ready for starting.
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 (refer to wiring diagram).
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 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 indicator 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.
The engine is shut off by turning key to position "1" or "0".
The steering lock has an attached valve which is actuated by way of a cam when the key is turned. A vacuum box on injection pump is provided with a vacuum and the regulating rod of the injection pump is pulled to "stop".