We have recently been having some remodeling done at a currently not-occupied home. One of the things done was a brand new breaker was installed. Before the breaker was installed, our HVAC was working, including a new (Smart with C-wire) thermostat. Now it isn't working at all. I've confirmed there is power going to the HVAC unit, although I'm less certain it is actually working correctly.
In diagnosing the problem, I immediately suspected the transformer could be the problem, as I have had issues with these in the past. I measured the AC voltage across this transformer, measured from the two bottom wires (Black and yellow), and saw 0. I measured it from each of them to the casing ground and measured 120. I saw no voltage between the two in the back (Red and blue).
Bottom line, I suspect one of 3 things is wrong, and I'm wondering if you can help me figure them out, or if it is something else entirely. Either the power was wired wrong to the unit, or the transformer is blown, or I'm measuring voltage wrong and there's a problem in a different area.
The box this was in, with some schematics, if it helps anything.