U3 - Check operation not executed or transmission error (Indoor/Outdoor Unit)

What does U3 mean?

The system has failed to complete its initial check operation, or there's a communication error between the indoor and outdoor units.

• Communication wiring issue
• Incorrect initial setup
• Faulty control board

Click steps to track your progress.

1. 1

   Turn off power to both indoor and outdoor units.

2. 2

   Verify that the communication wiring between the units is securely connected.

3. 3

   Restore power and allow the system to restart.

4. 4

   If the error code persists, a professional technician is needed.