Thermo King 098203, Maintenance Manual

Page: 249 / 264

Diagnosis: Troubleshooting, Warnings and Alarm Codes
247
98 Compressor Sensor Short Circuit
• When the sensor circuit resistance is below 550
Ω
.
• Indicates:
• Short circuit.
• Defective or wrong sensor.
• Defective wiring.
• Defective controller.
• 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 (M
Ω
) 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 86000
Ω
@ 25°C.
• Normal condition measuring with
disconnected sensor is
-
475k
Ω
@-10°C,
- 280k
Ω
@0°C,
- 171k
Ω
@+10°C,
- 135k
Ω
@+15°C,
- 107k
Ω
@+20°C.
• The valid measuring limit for this sensor is
-25°C(approx 1M
Ω
) +185°C(approx 550
Ω
).
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.
Alarm Codes, Descriptions and Corrective Actions (Continued)
Code Description Corrective Action