Without any scenarios to mess around with locomotives turned off, I didn't notice that the compressor on 166 and HST will work even if the engine is off until replaying tutorials on a different profile to see if that achievement works. Basically, as long as SimuGraph is on, the locomotive will start to charge the MR and MR pipe. The compressor shouldn't run if the engine is off...it kinda needs power from the electronics, or is actually connected to the crankshaft. Not sure the case on all the UK locomotives, but it needs the engine! (I sorta would expect SimuGraph to respect that by default...)