The U8 error code in air conditioning systems is most commonly associated with issues in activating the indoor unit’s fan motor.
This fan motor operates with electronically controlled speed, using two crucial signals:
- The fan motor speed sensor signal.
- The zero-crossing signal from the alternating current (AC) wave that powers the current sensor.
The zero-crossing signal is vital for synchronizing the motor’s operation with the AC wave phase, ensuring precise fan speed control.
- When the user sets the fan to high speed, the zero-crossing signal is detected, and power is immediately supplied to the motor.
- When set to low speed, the zero-crossing signal is also detected, but power is delayed by a few milliseconds before reaching the motor. This delay reduces the motor’s speed, allowing precise fan speed control.
Common Causes of the U8 Error Code
Many brands associate the U8 error code with issues in the zero-crossing signal. Examples include Mirage, Trane, Sharp, and other manufacturers.
When there is a problem with the zero-crossing signal, the U8 error code is triggered. Solving this issue can be complex, but the following steps are recommended:
Troubleshooting Steps
- Power Cycle the Unit:
Disconnect the unit from the power source for several minutes and then reconnect it. This can reset the system and clear the error if it was caused by a temporary malfunction. - Voltage Check:
Ensure that the power supply from the external electrical network is within the correct range. Acceptable values should be within ±10% of the nominal voltage. For example, if the nominal voltage is 110 V, issues may arise if the voltage drops below 100 V. - Inspect Electrical Connections:
Check the electrical connections powering the fan motor, focusing on the thicker cables. Ensure that there are no loose or damaged connections. - Examine the Speed Sensor:
Inspect the thin wires of the fan motor speed sensor to ensure they are properly connected and in good condition. - Manual Motor Check:
With the unit powered off, manually rotate the motor shaft to ensure it spins smoothly without obstructions. Difficulty in turning the motor may indicate mechanical problems that need resolution. - Visual Inspection of the Control Board:
Perform a visual inspection of the electronic control board to identify any damaged or abnormal components. Replace any faulty components as needed. - Replace the Electronic Board:
If all other steps fail to resolve the error, replacing the indoor unit’s electronic control board may be necessary.
Additional Considerations
For some Gree models, the U8 error code may be linked to a potential failure of the temperature sensor on the thin compressor pipe, which corresponds to the compressor discharge line.
If this is the case, inspect the sensor for any damage or disconnection and replace it if necessary.
