Error 18 — External communication error

What does 18 mean?

This error indicates that a signal has not been received from the external I/O PCB for 15 seconds after a signal was previously received. The outdoor unit shows no indication.

• Connection failure between the controller PCB and the external I/O PCB
• External I/O PCB failure
• Controller PCB failure

Click steps to track your progress.

1. 1

   Check for any loose or removed connections between the controller PCB and the external I/O PCB. Correct any abnormal conditions, referring to the installation manual.

2. 2

   Verify the condition of connectors, cables, and wiring on both the external I/O PCB and the controller PCB.

3. 3

   If simple connection fixes don't work, a technician may need to replace the external I/O PCB or the Controller PCB.