The Thermo King alarm 04, identified in yellow, initially suggests checking the discharge air temperature sensor in the involved area manually. Check the temperature manually and report the alarm at the end of the day.
Fault Code 4 Thermoking:
Regarding fault code 4 Thermoking, the most common causes are:
- Open circuit.
- Short circuit.
When the Thermoking system uses a PT1000-type sensor, the system module detects the open circuit problem when the resistance measurement of the sensor circuit is above 1300 Ω. The sensor short circuit is detected when the sensor circuit resistance is below 602 Ω.
Location of the problem causing alarm 04:
- Defective or incorrect sensor.
- Defective wiring.
- Defective regulator.
What to do with alarm 04:
- Check for damaged sensor cables.
- Check sensor connections to the controller.
- In some models, the sensor is a Pt1000, a two-terminal sensor that can be swapped without affecting measurement.
- Disconnect the sensor and, with a multimeter in the Ω position, measure the electrical resistance between the two sensor cables.
- The sensor cannot be examined without disconnecting it.
- When the sensor is a Pt1000, it has a positive temperature coefficient. This means that the sensor’s electrical resistance increases with temperature.
- The sensor is calibrated to have a resistance of 1,000 Ω at 0 °C.
- Normal resistance values with the PT1000 sensor can be seen in the following table:
| Temperature °C | Resistance Ω |
|---|---|
| -10 °C | 960 Ω |
| 0 °C | 1,000 Ω |
| +10 °C | 1,039 Ω |
| +15 °C | 1,058 Ω |
| +20 °C | 1,078 Ω |
| +75 °C | 1,300 Ω |