Troubleshooting a Thermo King APU That is Not Working

The Thermo King APU is a vital component in many trucks, providing heating, cooling, and electrical power when the main engine is turned off. However, like any other mechanical system, it can encounter issues that require troubleshooting. In this article, we will discuss a common problem with the Thermo King APU where it fails to work and how to diagnose and potentially fix the issue.

Identifying the Problem: One of the most common signs of a malfunctioning Thermo King APU is when it displays an error message on the screen, such as “TRI” (short for “Try”). This error message indicates that the APU is unable to complete its system checks and is stuck in the initial stage. Additionally, the APU may not turn on, and the heat, AC, and fan may not function properly.

Inspecting the Fuse: To begin troubleshooting, it is essential to check the fuse located on the motherboard of the Thermo King APU. In some cases, a burned or melted fuse can be the cause of the problem. Carefully remove the cover of the APU and locate the fuse. If the fuse appears damaged or melted, it is likely the culprit behind the APU malfunction.

Replacing the Fuse: If the fuse is indeed burned or melted, it is necessary to replace it with a new one. Ensure that the replacement fuse has the same specifications as the original fuse, such as the correct amperage rating. In this case, a 50-amp fuse is required. Carefully insert the new fuse into the designated slot, making sure it is securely in place.

Further Troubleshooting: After replacing the fuse, it is time to test the Thermo King APU to see if the issue has been resolved. Turn on the APU and observe if it goes through the system checks without getting stuck at the “TRI” stage. Check if the heat, AC, and fan are functioning correctly. If the APU still fails to work or the fuse continues to burn out, additional troubleshooting steps may be necessary.

Possible Causes and Solutions:

  1. Microwave Interference: The user mentioned the possibility of the microwave causing the fuse to burn. While it is unlikely, it is worth considering. Ensure that the microwave is properly connected to separate batteries and not causing any electrical issues.
  2. Coolant Temperature Sensor: Another potential cause of the APU malfunctioning is a faulty coolant temperature sensor. If the sensor is reading incorrect temperatures, it may prevent the APU from operating correctly. Consider checking and replacing the coolant temperature sensor if necessary.
  3. Fan Issues: The user discovered that the condenser fan was not working correctly. A malfunctioning fan can lead to overheating and trigger the APU’s shutdown code. Inspect the fan for any damage or blockages and replace it if needed.

When a Thermo King APU displays an error message and fails to work, it can be frustrating and inconvenient for truck drivers. By following the troubleshooting steps outlined in this article, such as checking the fuse, replacing it if necessary, and addressing potential causes like microwave interference, coolant temperature sensor issues, or fan malfunctions, it is possible to diagnose and potentially resolve the problem. However, if the issue persists, it is recommended to seek professional assistance from a Thermo King service center or a qualified technician.

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