My 18 month old Bryant Evolution A/C giving this message on thermostat. Malfunction Alert. Error code: indoor unit communication fault 255 events active. What does this mean? How to reset? A/C not working at this time.

For some reason the user interface(thermostat) has lost communication with the fan coil. Loose wire connection at thermostat or control board will do it. Or a control board going bad. The system should be under warranty have your service company check it out.

You are correct. It was the control board, which got moisture on it from a small pinhole opening. The installer said it was his error (duh) and has taken care of it.