Abnormal temperature of heatsink

What does U5 mean?

This fault is triggered when the heatsink thermistor (TH8) detects an abnormally high temperature, specifically 183˚F or above. This indicates inadequate cooling of the power module, potentially due to fan malfunction, airflow obstruction, or high ambient temperatures. Prolonged operation under this condition can lead to damage to the power circuit board or other components.

Complete Troubleshooting Guide

1. 1

   Inspect the outdoor fan motor for any signs of locking or failure. Ensure the outdoor unit's air flow path is clear of any obstructions that might impede cooling.

2. 2

   Verify the ambient temperature around the outdoor unit is within acceptable limits, considering that an upper limit of 114˚F is specified. Remove any external factors causing excessive temperature rise.

3. 3

   Perform a power cycle; if the fault changes to U6 instead of U5, follow the troubleshooting steps for U6. Otherwise, check the TH8 thermistor.

4. 4

   Measure the resistance value of the TH8 thermistor or check its temperature reading via microcomputer (refer to sections 10-6 and 10-10).

5. 5

   If other checks are inconclusive or components are deemed faulty, replace the outdoor power circuit board or the outdoor controller circuit board.