Dark blue wire to switch from A/C/Heater controls is energized in Max A/C and Normal position only I believe. Temperature control switch then controls power to Magnet clutch (at least on my 68 Dart with factory air). It should not always be energized from the controls, in mine it was also energized in the Off position, but not Heat and Defrost setting.
To correct this in a way that I actually preferred after I thought of it I added a push button switch switch with a micro relay inline on the blue wire from the controls to the evap temp switch so I can turn the compressor on/off if I want air from the vents without running the compressor (like in the rain when I don't want to open the windows). Doing this the evap temp switch still controls the compressor actually cycling but I control if I want it on at all. If I had to do it over again I would have powered my switch and relay directly off the power into the controls so I could also turn the compressor on in the Defrost setting like in modern car to dehumidify the air blowing on the windshield as well.
Downside of this is obviously I could forget and leave the compressor running when I don't want it too, but the switch is illuminated and it's pretty obvious when the compressor is running. Obviously everything powers down when the ignition is off so no danger of draining the battery.