4-38 4181383 First Edition
ELECTRICAL
4
Instrumentation Circuit—Theory of
Operation
Power Circuit
Unswitched power is available from the starting motor
battery terminal to 50 amp thermal circuit breaker battery
terminal. Unswitched power is available from 50 amp
thermal circuit breaker battery terminal to key switch
terminal A and control module terminal J3-6.
When the key switch is turned to the run position, voltage
is provided from key switch terminal B to control module
switch power input terminal J3-2, powering up the control
module. Voltage is also provided from key switch terminal
B to control module select 2 input terminal J4-2,
activating the input. With the select 2 input activated, the
control module selects the software program for this
machine. This allows the control module to be used in
more than one machine.
With the internal switched power relay energized,
switched power is available from switched power relay
terminal 87 to control module terminal J3-5. Switched
power is available from control module terminal J3-5 to
splice 100. From splice 100, switched power is available
to the Hydraulic oil level switch.
With the internal switched power relay energized,
switched power is available from switched power relay
terminal 87 to control module terminal J3-3. Switched
power is available from control module terminal J3-3 to
splice 90. From splice 90, switched power is available to
the traction control switch and then from the traction
control switch to the hydraulic oil level light.
Switched power is available from splice 90 to engine
temperature gauge and then from the engine
temperature gauge to the fuel gauge.
Hour Meter
The fuel gauge provides switched power to the hour
meter, and the hour meter starts logging hours.
Engine Oil Pressure Light
When the engine oil pressure is below 7 psi (0.483 bar),
the engine oil pressure switch contacts close. With the
switch contacts closed, a ground is provided to the
engine oil pressure light, turning on the light.
With the engine oil pressure switch closed, a ground is
also provided from the switch to control module engine oil
pressure input terminal J2-1, activating the input. With
the input activated and after a 30 second delay the
control module does not allow the mow circuit to operate.
At the same time the control module horn output terminal
J3-10 provides voltage to the horn, turning on the horn.
The horn sounds for 5 seconds and then chirps every 3
seconds.
Hydraulic Filter Pressure Light
The hydraulic filter switch is a differential pressure switch.
The switch closes when there is a 25 psi (1.724) drop
between the inlet and outlet pressures of the filter.
When the hydraulic filter pressure switch closes, a
ground is also provided from the switch to control module
hydraulic filter pressure input terminal J2-2, activating the
input. With the input activated and after a 5 second delay,
control module hydraulic filter pressure light output
terminal J2-8 provides a ground to the hydraulic filter
pressure light, turning on the light. At the same time the
control module horn output terminal J3-10 provides
voltage to the horn, turning on the horn. The horn sounds
for 5 seconds and then chirps every 3 seconds. The
control module does not allow the mow circuit to operate
when the hydraulic filter pressure switch input is
activated.
Fuel Gauge
The float attached to the fuel level sender moves as the
fuel level changes to various levels. The resistance of the
fuel level sender changes in relationship to the position of
the float. As the resistance changes, the amount of
current flowing through the circuit changes and the
amount of current flowing is indicated by the fuel gauge.
Engine Temperature Gauge
The engine temperature sensor resistance changes in
relationship to the engine coolant temperature. As the
engine temperature sensor is heated, the resistance of
the sensor changes from a high resistance to a low
resistance. The amount of resistance in the circuit
controls the amount of current flowing through the engine
temperature gauge. The amount of current flowing
through the circuit is indicated by the gauge as a
temperature measurement.
The voltage drop across the temperature sensor is
provided to control module engine temperature sensor
input terminal J2-12. The amount of voltage across the
sensor also has a relationship to temperature.
When the engine coolant temperature reaches 230°F
(110°C), the voltage across the sensor signals the control
module to not allow the mow circuit to operate and sound
the horn. The horn sounds for 5 seconds and then chirps
every 3 seconds. There is a 30 second delay before the
control module activates the horn circuit.
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