Re: WHERE TO DRAW THE LINE
Here in California, a contractor may perform work outside of his trade if the work in question is both "incidental and supplemental" to his own work.
Of course that's open to interpretation, from what I've see this state usually allows the HVAC tech to work on any electrical EQ from the load side of the disconnect in, but not the disco itself. Internal fuses, contactors, are fair game.
We also have a big problem here with residential HVAC guys thinking this allows them to run their own circuits, which it does not. Last year I went to court along with a customer to testify on just such an installation. The HVAC contractor who refused arbitration because he was sure he was in the right, ended up paying for the entire cost of the repair (this genius had tapped a dryer circuit in the attic to feed the condensing section, nice.).
Best bet if you're not sure is to check with your AHJ.