TANK AS-FUEL 1301254 - Caterpillar

Illustration 1 g01076569
Thermistor Assembly, Part Number 229-3138Each of the four screed plates is equipped with a thermistor assembly. The optional extension screed plates are not equipped with a thermistor assembly. The electrical resistance of the thermistor sensor will change as the temperature of the screed plate changes. This input information is used by the CAT Electric Heat Control in order to monitor and maintain the selected temperature setting. In the event that the thermistor malfunctions, the control will turn OFF the power for the section electric elements. In order to verify that the thermistor sensor has failed, perform one of the following procedures.Reference: A simplified electrical schematic of the electric heating system for the screed is displayed in the System Operation, "Electric Heat System" section of this manual. For a complete screed electrical system schematic, refer to Electrical System Schematic, KENR3707.One way to check a thermistor sensor is to exchange the suspect sensor with a sensor from a screed plate section that is known to be operating correctly. After the sensors are exchanged, if the section that was malfunctioning works correctly, replace the malfunctioning sensor. This requires the partial disassembly of two screed plate assemblies. If this is not a desired method for checking the sensor, a procedure for checking the electrical resistance of the thermistor sensor is given below.When the screed plate temperature increases, the electrical resistance of the thermistor sensor decreases. At cooler temperatures, the electrical resistance of the thermistor sensor increases. Table 1 displays some temperatures and the expected thermistor resistance.
Table 1
Thermistor Sensor Resistance    
Temperature    Resistance in Ohms    Tolerance    
0 °C (32 °F)     319,900     11.8%    
10 °C (50 °F)     196,800     11.0%    
25 °C (77 °F)     100,000     10.0%    
40 °C (104 °F)     53,670     10.9%    
55 °C (131 °F)     30,220     11.8%    
60 °C (140 °F)     25,200     12.1%    
70 °C (158 °F)     17,770     12.6%    
80 °C (176 °F)     12,740     13.1%    
100 °C (212 °F)     6,860     14.1%    
120 °C (248 °F)     3,907     15.0%    
135 °C (275 °F)     2,646     15.6%    
150 °C (302 °F)     1,837     16.2%    In order to check that the thermistor sensor is working properly, perform the following procedure.
Turn the key switch to the OFF position. Ensure that the machine is secured in order to prevent any movement.
Allow the screed plates to cool down to the ambient air temperature.
Remove the covers for the screed plate in order to allow access to the thermistor sensor connector. Disconnect the thermistor sensor connector from the machine harness connector.
Use an ohmmeter in order to check the resistance of the thermistor. Place one meter lead on one terminal of the sensor connector. Place the other meter lead on the other terminal of the sensor connector.
Observe the resistance value on the ohmmeter. Record the measurement. Refer to Table 1. Verify that the recorded measurement is