The behavioral logic of the ECO422D is described in table 2-3 on page 2-8 of the ECO422D user manual (also shown below). One general rule of thumb is that the unit will NEVER automatically switch to a bad signal; it can only switch to a bad signal if told to do so by the user. As shown on line 4 of the table below, if both the primary and backup signals are good, no preference is given to either and the unit will not switch back to the primary; the change back to primary must be manually applied by the user. Ln. # Power User Config Mode Switch Button Primary is… Backup is… Output (auto mode) Output (manual mode) 1 On Normal No Switch Bad Bad No Switch No Switch 2 On Normal No Switch Bad Good Backup No Switch 3 On Normal No Switch Good Bad Primary No Switch 4 On Normal No Switch Good Good No Switch No Switch 5 On Normal Switch Bad Bad Switch Switch 6 On Normal Switch Bad Good Backup Backup 7 On Normal Switch Good Bad Primary Primary 8 On Normal Switch Good Good Switch Switch 9 On Override No Switch Bad Bad No Switch No Switch 10 On Override No Switch Bad Good Backup No Switch 11 On Override No Switch Good Bad Primary No Switch 12 On Override No Switch Good Good No Switch No Switch 13 On Override Switch Bad Bad Switch Switch 14 On Override Switch Bad Good Backup Switch 15 On Override Switch Good Bad Primary Switch 16 On Override Switch Good Good Switch Switch 17 Off n/a n/a n/a n/a Primary Primary