Charging a 12V battery bank while using it
There is no problem with having a load drawing power while a charger is charging the batteries. The charger is pushing power into the system and the A/C is taking it out again. Most of the power will be going straight from the charger to the A/C, but that just means that your battery array will take longer to charge as it'll only be getting charged at 17A as opposed to 100A (100A-83A). This is the same as when you use your laptop or phone while it's plugged in.