WHEEL AS 3865396 - Caterpillar

Temperature Sensor for the Evaporator Coil (Thermistor)
Illustration 1 g00481655
Heater/air conditioner unitTemperature sensor (27) (thermistor) is a semiconductor. When temperature increases, resistance decreases. On the other hand, when temperature decreases, resistance increases.Temperature sensor (27) (thermistor) is located at the discharge side of evaporator coil (16). Sensor (27) detects the temperature of the cooled air as the air is discharged from evaporator coil (16). The sensor then sends the signal back to the amplifier in the control module.The control panel switches the air conditioner clutch OFF when the temperature is under 3°C (37°F). When the air temperature becomes 4°C (39°F) or more, the air conditioner clutch is turned ON. This sensor also prevents the evaporator from freezing.
Illustration 2 g00520124
Graph of resistance values
Table 1
Resistance Values for the Temperature Sensor at the Evaporator Coil (Thermistor)    
Temperature (°C)    Resistance (Ohms)    
Minimum Medium     Maximum    
-10
    17.5     18.2     19.0    
0     11.0     11.4     11.7    
10     7.04     7.32     7.61    
20     4.63     4.86     5.09    
30     3.14     3.31     3.50    
40     2.18     2.32     2.46    Measure the resistance of the sensor by disconnecting harness (11) at control module (20) .Reference: Refer to Testing and Adjusting, "Air Conditioning System Schematic" for the proper pin locations.Reference: Refer to Table 1 for the proper figures.If the resistance values agree with the values from Table 1, sensor (27) is good.If the resistance values do not agree with the values from Table 1, replace the temperature sensor (thermistor).