1.18.2. Battery/Starting Circuit. The engine starting
circuit is controlled by the fuel shutoff solenoid and start
relay. The fuel shutoff solenoid is energized through
contacts in the high temperature shutdown sensor and
the DCA engine test switch. The start relay is energized
through relays controlled by the control handles.
Electrical power at 12 VDC is supplied from CB1 to the
normally closed contacts of the high temperature
shutdown sensor. When engine temperature is below
220°F (105°C), the 12 VDC passes through the
temperature shutdown sensor to the DCA engine test
switch. The DCA ENGINE CRANK switch spring return
the closed position and is only used when testing the,
engine. The electrical power passes through the
ENGINE CRANK switch to energize the fuel shutoff
When engine temperature is above 220°F (1050C), the
high temperature shutdown sensor contacts open and
prevent the fuel shutoff solenoid from being energized.
This cuts off fuel to the engine and prevents the engine
from being started. In emergencies, the high
temperature manual override button may
be pushed and held to allow starting the engine. The
override button supplies power to the engine fuel shutoff
solenoid from CBI as long as the button is held. This
bypasses the engine high temperature shutdown sensor.
Electrical power from CB1 is also routed to both control
handles. With the left control handle in the center detent
position, the control handle sends a 12 VDC signal to the
contacts of relay R3. With the right control handle in the
center detent position, the control handle passes a 12
VDC signal which energizes relay R3. This closes the
contacts of relay R4. With relay R4 energized, the start
position of the ignition switch sends 12 VDC through the
contacts of relay R4. This signal energizes the coil of the
start relay. The batteries send 24 VDC through the
contacts of the start relay, engaging the starter solenoid
and turning the starter.
Releasing the ignition switch from the "START" position
removes the voltage from the coil of the start relay and
disengages the starter.