Abnormal Heatsink Temperature

What does U5 mean?

The heatsink thermistor (TH8) detects an abnormal temperature, either too low (below -40°F [-40°C]) or too high (above 183°F [84°C]). This indicates a potential issue with the outdoor fan, restricted airflow, excessive ambient temperature (above 114°F [46°C]), or a fault in the thermistor or associated circuit boards.

• Heatsink temperature detected by the sensor is abnormally high.
• Overheating of electronic components on the heatsink.
• Blocked airflow to the heatsink.
• Fan failure for heatsink cooling.
• Excessive ambient temperature.

Click steps to track your progress.

1. 1

   Check the outdoor fan for proper operation, ensuring it is not locked or obstructed.

2. 2

   Inspect the air flow path around the outdoor unit for any clogging or restrictions that could impede cooling.

3. 3

   Verify the ambient temperature around the outdoor unit to ensure it is within the specified operating limits (e.g., upper limit 114°F [46°C]).

4. 4

   Measure the resistance value of thermistor TH8 and compare it to expected values for the measured temperature.

5. 5

   If the outdoor fan, airflow, and thermistor are confirmed normal, replace the outdoor power circuit board.

6. 6

   If fan drive is faulty, replace the outdoor controller circuit board.