We replaced the Adaptive Defrost Board after following advice and determining the "5 door-switch clicks in 6 seconds" manual-defrost command wasn’t working. No joy, so we defrosted manually to give it a clean start. Still no joy, so we called a local repairman.
He replaced the defrost terminator and now all is good. I found the terminator on the electrical diagram, but no part for it on the online part-to-partnumber diagrams.
I’ve got no idea if the original board was bad or not, or if it’s worth trying the original board again to see. It looks fine. Is there any chance that trying the original board could hurt the new defrost terminator?