ELECTRICAL
10.10
FAN MOTOR CURRENT
DRAW
A current draw test provides a good indication of fan
motor condition. Worn or damaged fan motors will
draw more current, which causes a reduction in blade
speed and reduced cooling.
Fan Motor
Connect ammeter
between Or/Blk leads
Or/Blk
Fan
Motor
Harness
Or/Blk
Brn
Ammeter
1.
Disconnect the harness from the thermistor.
2.
Connect a DC ammeter in between the fan switch
harness wires as shown.
3.
Be sure fan blade is free to rotate.
4.
Turn ignition key and engine stop switch to “ON”
position. Read the current draw on ammeter with
fan running.
5.
If the fan motor draws more than 7.5 Amps,
continuous, replace the motor.
Fan Motor Current Draw:
Less Than 7.5 Amps
TEMPERATURE SENSOR
(THERMISTOR) OPERATION /
TEST
The thermistor relays a power signal to the ECM
depending on engine coolant temperature. Should the
thermistor fail open the engine Hot light and fan will
both come on. With engine cold, disconnect lead and
measure resistance of sensor between the two
Yellow/Black connector terminals. There should be no
continuity from the thermistor lead to engine ground.
See “Engine Temperature Controller” on Page 10.4
for additional information on thermistor operation.
SITUATION
OHMS
READING
DIAGNOSIS /
ACTION
Hot light ON &
Fan ON
Above 50k
Open Thermistor /
Replace Thermistor
Hot light ON
Below 178
Engine Overheat
or Bad Thermistor
THERMISTOR READING DURING OPERATION
Condition
Approx. Reading
(Min--Max)
Temperature
Hot Light
On
178
Ω
-- 190
Ω
215
°
F
(102
°
C)
Fan Off
296
Ω
-- 316
Ω
180
°
F (82
°
C)
Fan On
236
Ω
-- 251
Ω
195
°
F (91
°
C)
1.
Place thermistor in a water bath and thermometer
and submerse it to the base of the threads. Do not
allow threads to contact container or inaccurate
reading will result.
2.
Heat slowly and monitor the resistance at various
water temperatures with a thermometer or
Fluke
t
meter pyrometer.
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