Glad it helped Paul.
You want a wire to be able to tell if the engine is running so that when it isn't energized you can energize a circuit to trigger the AC pump.
If I understand you, wouldn't a feed from the alternator be your solution?
I don't really think I completely grasp what you want because in trying to imagine the design of your circuit, it seems a little complicated. But considering the things you have managed with your engine, I put NOTHING past you.
12V from alternator energizing a relay keeping it open. When the 12V disappears, relay closes, activating 12V from the battery to another relay which is controlled by your turbo timer.