Ok, talked to both mechanics that worked on A/C. First guy installed new compressor and the silver cylinder with the low line quick connect. He said he put oil in compressor and put on plate to keep oil from leaking out without hose.
Second guy installed high line, definitely ran a vacuum pull, and possibly added refrigerant (he can't remember but says he probably did before telling me to replace low pressure sensor).
System was not flushed (though first mechanic said everything looked fine) and we actually didn't end up replacing condenser or evaporator.
To clarify, do I need to disconnect the battery to allow the compressor to engage or does resetting the code on CRT do the same thing?