Safety: Unplug the unit before any disassembly. Do not attempt to reprogram the board without proper tools and firmware.

Steps to address E9:

Power reset: Unplug the air conditioner for at least 10 minutes to allow capacitors to discharge and the control to fully reset. Plug back in and test.
Check power quality: Use a surge protector rated for air conditioners or a dedicated circuit. Avoid sharing the circuit with heavy loads.
Inspect control board: Remove the control box cover and visually inspect the main PCB for burn marks, bulging capacitors, or corrosion.
Connector check: Reseat all connectors on the main board, including power input, sensor harnesses, and display harness.
Board replacement: If E9 persists, the EEPROM or microcontroller on the board is likely damaged. Replace the main control board with an Arctic King-compatible replacement. Transfer any jumpers or configuration plugs from the old board to the new one as instructed in the service literature.

Display shows E9; unit may not start or may shut down unexpectedly, often after a power outage or surge.

Possible Causes