What alt do you have brand HO or stock?
Module should have no affect on your AC which is on a totally different circuit. So no answer for that. If your seeing 15.8v its gettin a low charge signal from your car/batteries. 15,8 @ cold start is ok it should back down to 15,4 or so when hot. 15,8 for comp would be fine, 4+ battery banks need the extra volts and can dissipate it .
MLA