I took control box to computer and uploaded sketch with shorter venting cycle. Relays fired as expected. I reconnected to farm and something wasn’t right – servo sounded to be struggling. It worked fine in testing.
Transformer cutout and a telling smell appeared. I thought it was in the control box but that was fine. I then lifted lid on farm and smoke came out. One of the sensors was burnt out.
This is where my limited novice knowledge shows. I’ve worked through wiring and think I’ve found problem. Having belled out ground through supplies I decided to share 5v and 12v ground to farm to transformer common. It sounds dumb now but that’s learning for you. Something to do tomorrow now. And I’ll delay livestock order.