OPERATOR'S MANUAL MAINTENANCE

Section C - Electrics
Basic System Operation
Viscous Fan
C-74 C-74
9803/9880-3
Viscous Fan
865670
Fig 70.
Operation
The cooling pack temperature is controlled by an
electromagnetically controlled viscous coupling fan. The
electromagnetic clutch which drives the fan speed is
controlled by a PWM signal from the ECU1.
Engine water and hydraulic oil temperature are monitored
by the ECU1. As their temperatures change, the ECU1 will
vary the PWM signal to the electromagnetic clutch. This
changes the speed of the fan. As the temperature
increases the PWM signal will decrease to drive the fan
faster. If the PWM signal is lost to the electromagnetic
clutch the fan will run at full speed.
The output PWM signal will drive the fan RPM to that set
by the highest temperature as determined by the graph.
K
Fig 71. ( T C-74).
823271
Fig 71.
X = Fan Speed +/-50rpm.
Y = Oil Temperature.
Z = Water Temperature.
I/p 10 (A-38)
I/p 1 (A-19)
I/p 2 (A-18)
O/p 8 (C-3)
FAN DUTY
CAN
Data
ECU 1
EMS
A
B
C
D
A Viscous fan solenoid
B A/C switch
C Hydraulic oil temperature
D Engine coolant temperature
0
25
50
75
100
10 20 30 40 50
 C
% PWM Signal
% Pulley Speed
60 70 80 90 10
0
0102030405060708090100
X
Y
Z