cooling fan problem

touring, non turbo, auto, 100k miles. Car always ran cool, first line on temp gauge. Then car ran at halfway mark on temp gauge, fan at low speed. But when I turn a/c on fan does not speed up to fast cycle, will over heat in city with a/c on. With a/c off car is ok at halfway mark on temp gauge...

Please advise what should be the correct resistance reading when checking the hi/low resistor for the radiator fan 2011 dodge grand caravan i know that it should not reading OPEN Can anyone please check the resistor across the Resistor on a newer, working correctly late model radiator...