ELECTRICAL
10.6
OIL COOLER FAN CONTROL
Battery Voltage
OIL COOLER FAN CIRCUIT
Hot light and fan “on” with leads connected
Electronic
Module
GThermistor resistance decreases as
temperature increases
GBoth fan and hot light should be on with
thermistor leads shorted together
(low resistance)
GFan blade should rotate drawing air in
through cooler (blowing on engine)
THERMISTOR -- RESISTANCE VS.
TEMPERATURE
Tempera-
ture
Resist-
ance ±
20%
Fan ON/
OFF
Hot Light
ON/OFF
77° F(25°
C)
100KW Fan OFF
240° F
(116° C)
3.5KW Fan OFF
260° F
(127° C)
2.5KW Fan ON
290° F
(143° C)
1.6KW Fan ON Hot Light
ON/OFF
THERMISTOR / FAN
CONTROL
TEST
GT urn ON and engine stop switch to RUN.
GTest voltage on R/W wire to ground -
R/W wire should have 12 Volts DC
(battery voltage)
GShort thermistor leads together - fan
and hot light ON? (If not, test hot
light, fan motor and circuit)
GDisconnect thermistor wires and test the
resistance of the thermistor (refer to
temperature/resistance table).
Replace thermistor if out of specified
range.
GReplace the module and test system.
FAN MOTOR CURRENT
DRAW
TEST
Connect ammeter leads
between exposed
Orange/Black terminals at
fan connection.
Connect only the Red/White
terminals at fan connection.
A current draw test will provide a good indication of fan
motor condition. A worn or damaged fan motor will
draw more current, which causes a reduction in blade
speed and reduced cooling.
1. Turn key t o off.
2. Disconnect the thermistor.
3. Reconnect fan motor connector to place a DC
ammeter in series as shown in the Illustration.
4. Be sure fan blade is free to rotate.
5. Turn ignition key and engine stop switch to “ON”
position. Read the current draw on ammeter with
fan running.
6. If the fan motor draws more than 6.5 Amps,
replace the motor.
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