a/c problem, 95 Caprice with HD cooling.

Hi everybody. I have a question about operation of a/c on a 1995 Caprice with a heavy duty cooling system which comes with a tow package option (i.e. car has one belt-driven fan and one electric fan). Does someone know whether electic fan has to turn on when I turn on the a/c ? I experience a problem that a/c blows cold only if I am driving on an interstate. In a slow traffic it is kind of inefficient.