ELECTRICAL
10.24
TEMPERATURE SENSOR
(THERMISTOR)
TEST
If the thermistor circuit is 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 or very high resistance (see chart).
See “Engine Temperature Controller” on Page 10.5
for information on thermistor operation.
SITUATION
OHMS
READING
DIAGNOSIS /
ACTION
Hot light ON &
Fan ON
Above 50k Open Thermistor /
Replace Thermis-
tor
Hot light ON Below 178 Engine Overheat
or Bad Thermistor
THERMISTER READING DURING OPERATION
Condition
Approx. Reading
(Min--Max)
Temperature
Hot Light
On
178Ω -- 190Ω 215° F
(102° C)
Fan Off 296Ω -- 316Ω 180° F(82° C)
Fan On 236Ω -- 251Ω 195° F(91° C)
FAN MOTOR CURRENT DRAW
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.
Fan Motor
Brn
Org/Blk Org/Blk
1. Disconnect the harness from the fan motor.
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,
replace the motor.
Fan Motor Current Draw:
Should Be Less Than 7.5 Amps
CAUTION: Keep hands away from fan blades
during this procedure. Serious personal injury
could result.
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