The 2 fans are seperate.

The Aux. fan turns on when the AC is on full blast, if the car reaches higher temps towards 100 degrees celsius to aid in cooling the engine down, and under circumstances when instructed.

I've driven in SoCal heat for almost 2 summers without a working AUX fan. Just keep all cooling components in top condition, keep your coolant as fresh as factory suggests, and you should be fine. Thats all I've done.