[TJ Clark]

Based upon your description, this could be a whole host of different causes, so thanks for being open to collecting data to narrow the diagnosis.

I am pretty sure you have basement SCS units. Would you confirm?
Are you comfortable working in a control box with live electrical circuits?
Do you have a clamp on ammeter?



But you know me, In God we trust, everybody else bring data.


Yes, yes and yes. 
I'll do the testing later today. Thanks.