Textron JACOBSEN GP400, Technical/Repair Manual

Page: 67 / 354

ELECTRICAL
4252490-Rev A 4-15
4
Diesel Engine Circuit—Theory of
Operation
Power Circuit
When the key switch is turned to the run position, voltage
is provided from key switch terminal B to control module
terminals J1-2, J2-11, and J2-12, powering up the control
module.
Switched power is also provided to the fuel pump. With
switched power provided to the fuel pump, the fuel pump
starts to operate. (See “Power Circuit—Theory of
Operation” on page 4-14.)
Interlock Circuit
To start and operate the engine, the following must
occur:
• Seat switch in the on position (operator on seat)
• Park brake switch in the on position
• Mow switch in the off position and/or mow/transport
switch deactivated (lever in run position 2)
When the seat switch is in the on position, voltage is
provided to the control module seat switch input terminal
J1-7, activating the input.
When the park brake switch is in the on position, voltage
is provided to the control module park brake switch input
terminal J1-11, activating the input.
When the mow switch is placed in the off position, or the
mow/transport lever is in run position 2, voltage is not
provided from the switch to the control module mow
switch input terminal J1-5, indicating the switch is in the
off position.
Glow Plug Circuit
When the key switch is turned to the start position,
voltage is provided from key switch terminal C to the
control module start input terminal J1-6, activating the
input. With the start input activated, voltage is provided
from the control module glow plug relay output terminal
J2-3 to glow plug relay terminal 86, energizing the relay.
With the relay energized, voltage is switched between
relay terminals 30 and 87 and is provided to the glow
plugs, heating the glow plugs.
Glow plug activation is scaled between 1 and 8 seconds;
the duration is determined by the engine temperature
sensor. When the engine coolant temperature is 122° F
(50° C), the engine temperature sensor provides 8.68
volts to the control module engine temperature input J2-1
and the glow plugs are activated for 1 second. When the
engine coolant temperature is 32° F (0° C), the engine
temperature sensor provides 10 volts to the control
module engine temperature input J2-1 and the glow
plugs are activated for 8 seconds (maximum).
The control module also flashes the alarm light at
1-second intervals while activating the glow plug circuit.
Start Circuit
With the key switch held in the start position, the control
module start relay output terminal J2-4 provides voltage
to start relay terminal 86, energizing the relay. With the
start relay energized, voltage is switched between relay
terminals 30 and 87 and provided to the starter motor
solenoid, energizing the solenoid. With the starter
solenoid energized, voltage is switched between the
starter solenoid contacts to the starter motor, engaging
the motor.
At the same time, the control module engine run output
terminal J2-5 provides voltage to the fuel shutoff timer
input terminal, activating the input. With the fuel shutoff
timer input activated, the engine continues to operate.
The control module engine run output terminal also
provides voltage to the hour meter, and the hour meter
starts logging hours.
Run Circuit
When the operator is on the seat (seat switch in the on
position), the control module allows the engine to
continue to operate when the park brake switch is in the
off position. The control module will deactivate the engine
run output terminal if the operator leaves the seat with
the park brake switch in the off position.
When the park brake is engaged (park brake switch in
the on position), the control module allows the engine to
continue to operate when the operator is off the seat. The
control module will deactivate the engine run output
terminal if the park brake is disengaged with the operator
off the seat.
When the control module deactivates the engine run
output terminal, voltage is no longer provided to the fuel
shutoff timer input terminal, deactivating the input. With
the input deactivated, the fuel shutoff timer output
terminal provides voltage to the fuel shutoff solenoid for
approximately 7 seconds. With the solenoid energized,
fuel is prevented from flowing to the engine, and the
engine stops operating. After approximately 7 seconds,
the fuel shutoff timer de-energizes the solenoid.
Charging Circuit
With the engine running, switched power is provided to
the alternator field terminal, exciting the alternator. With
the alternator field terminal excited, the alternator
produces three-phase alternating current (AC). The AC
voltage is provided to the alternator’s internal voltage
regulator.
When the battery voltage is low, the voltage regulator
provides a regulated voltage to charge the battery. When
the battery is fully charged, the regulator stops providing
regulated voltage to the battery.