Could someone explain to me the effects of running an ac with windows open? Specifically, why does the evaporator temp increase when the car ac is running with open windows.
With car windows open you have outside warmer air constantly entering the cab and the evaporator needs to work harder; actually to its max. In addition, you have the load of the AC compressor added to wind resistance from open windows.
You might get higher airflow if you just crack a window open. Lower air pressure inside the car can increase air flow.