97 Compressor Sensor Open Circuit MP4000

Description 

Compressor Sensor Open Circuit 

• When the sensor circuit resistance is above 3000kΩ. 
• Indicates: 
• Open circuit. 
• Defective or wrong sensor. 
• Defective wiring. 
• Defective controller. 

Corrective Action 

• Check for damaged sensor wires. 
• Check sensor connections at controller. 
• The compressor temperature sensor is a NTC – 2 wire sensor. The sensor is located/connected to the MP-4000 at connector J3 pin 13 and 14. CM-4000 upper left connector J3, 17 pin wide, pin number 1 is the right pin, seen at the backside of the controller. 
• The 2 sensor wires can be switched without affecting the measurement. 
• Disconnect the sensor, use an Ohm (Ω) measuring device, measure the electrical resistance between the two sensor wires. 
• The sensor can’t be examined without disconnecting it. 
• The electrical resistance towards chassis must be above meg ohm (MΩ) range. 
• The sensor is a NTC thermistor type - negative temperature coefficient, which in this case means that the resistance of the sensor decreases with temperature. 
• The sensor is defined to be 86000Ω@ 25°C. 
• Normal condition measuring with disconnected sensor is 
• - 475kΩ@-10°C, 
• - 280kΩ@0°C, 
• - 171kΩ@+10°C, 
• - 135kΩ@+15°C, 
• - 107kΩ@+20°C. 
• The valid measuring limit for this sensor is -25°C(approx 1MΩ) +185°C(approx 550Ω). 

NOTE: OPEN circuit state is not reasonable since open indicates high electrical resistance which with this type of sensor is possible at very low temperature. Instead -30°C is shown as temperature. The needed protection compressor temperature vice is at the high temperature end of the scale.