When your not running a/c the radiator fan kicks on at 220 or so degrees when you run the a/c the fan turns on because it has to pull air over the condensor in front of the radiator to cool the refrigerant which also cools the radiator at the same time. When your on the highway it stays around 190 because there is always airflow over the radiator. The temp may be slightly higher when you have the a/c on during highway driving than with it off because the condensor heats up the air before it flows over the radiator.
I'm not sure on the voltage part. someone else will prbly have input on that
