H. Quick-Start Preglow System (Model 123.1)
Operation of Preglow SystemH. Quick-start preglow system engine 615, 616, 617.91 in model 123.1
General
The essential components of the preglow system are the quick-start pencil element glow plugs, the preglow time relay and the preglow indicator lamp.
Note: On engine 615, 616, the pencil element glow plug G 5 is no longer installed.
Quick-start pencil element glow plugs
The quickstart pencil element glow plugs are designed for a voltage of 11 volts and are operated in parallel.
Preglow time relay
The preglow time relay is located in engine compartment at the left on wheelhouse.
After removing protective cap, the electric connections, as well as the 80-amp fuse are accessible.
The former temperature sensor in coolant circuit is no longer installed. Instead, the relay temperature or relay-ambient temperature is obtained by means of an NTC resistor in preglow time relay.
Functions of preglow time relay
The pregiow time relay comprises the following functions:
- Switching of glow current
- Ready-for-start indicator
- Safely shutoff
- Fault indicator
Switching of glow current
By actuation of key in position "2" (preglow, driving), the preglow time relay (voltage at terminal 15) is engaged. The power relay (a) closes the circuit from terminal 30 (positive) via fuse to pencil element glow plugs G1 - G5.
If the key is turned to position "3" (start), the power relay (a) remains attracted, activated by terminal 50. The glow period continues until the key is turned back to position "2".
Ready-for-start indicator
A temperature sensor installed in preglow time relay obtains the glow period.
When the glow system is switched on, the preglow indicator lamp in instrument cluster will light up.
If the required glow period, in dependence of the ambient temperature of the preglow time relay, is attained, the preglow indicator lamp goes Out and thereby indicates the ready-for-starting condition.
Safety shutoff
If there is no start within 20-35 seconds following indication of ready-for-starting condition, the glow current is interrupted by the safety shutoff. If another start follows, the glow system is again switched on for the duration of the starting period.
The safety shutoff is no longer a fixed condition. It is determined by the time up to ready-for-starting condition (preglow indicator lamp goes out) plus 20 to 35 seconds.
Fault indication
A fault in preglow system is indicated if the preglow indicator lamp is not lighting up when the key is actuated in position "2".
The following faults are indicated:
- Interruption of line to connection terminal 30.
- 80-amp fuse defective.
- Power relay in preglow time relay defective.
- Interruption of one or more lines to pencil element glow plugs.
- Interruption of one or more pencil element glow plugs.
Note: If tolerances of pencil etement glow plugs or of Reed relay (d) are unfavorable, response of fault indicator only if tvvo pencil element glow plugs are defective is acceptable.
Faults are indicated (pencil element glow plug resistance control) by comparing the current of pencil element glow plug Gi with current of remaining pencil element glow plugs G2-G5 (or G2-G4) connected in parallel.
The currents of the two lines to the pencil element glow plugs Gi and G2 up to G5 (or G2-G4) are rooted through two Reed relay coils with different numbers of wind ings connected opposite to each other.
If the current flow in both coils is the same, the magnetic fields will cancel each other and the Reed contact will not respond.
If the balance of the magnetic field is interrupted by the loss of one or several pencil element glow plugs, the Reed contact will close and the electronic system (b) will be activated.
The preglow indicator lamp switches off immediately and will therefore not light up when the preglowing begins.