Amp Fuse, Preheat Switch, Start/Stop Switch | Guardian Technologies 4270

Section 5

ENGINE DC CONTROL SYSTEM

14 AMP FUSE

WIRE 17 (FROM THE ENGINE CONTROL BOARD):

This panel-mounted Fuse protects the DC control cir- cuit against overload and possible damage. If the Fuse has melted open due to an overload, neither the priming function nor the cranking function will be available.

Figure5-4

This is the crank and start circuit. When the switch is set to start, Wire 17 is connected to ground via Wire

0.With Wire 17 grounded, a crank relay on the circuit board energizes and battery voltage is delivered to the starter contactor via Wire 56. The starter contac- tor energizes and its normally open contacts close allowing battery voltage through Wire 16 to the starter motor and the engine will now crank. With Wire 17 grounded, a run relay on the circuit board energizes and battery voltage is delivered to the Wire 14 circuit. Now the fuel pump, fuel solenoid, hourmeter, and field boost has battery voltage for operation.

WIRE 18 (FROM THE ENGINE CONTROL BOARD):

This is the engine stop circuit. When the start/stop switch is set to stop, Wire 18 is connected to ground via Wire 0. Circuit board action then opens the circuit to Wire 14, stopping fuel flow, causing the unit to stop.

WIRE 0:

Connects the switch to ground.

PREHEAT SWITCH

The diesel engine is equipped with glow plugs, one for each cylinder. When the preheat switch is pressed, voltage will go through the switch to the pre- heat contactor. The preheat contactor (normally open) now closes, allowing battery voltage to go to the glow plugs via Wire 157. Power from Wire 157 goes through a diode and changes to Wire 14. This Wire 14 goes to the circuit board powering the fuel pump, fuel solenoid, hourmeter, and field boost through another diode and resistor. The glow plugs now heat the engine combustion chamber, and the injector pump is primed with fuel for starting.

17 (START)