The fan will only kick on when the coolant goes beyond a certain temperature. I can't tell you what that is off the top of my head but I would guess probably around 220 or maybe a little more. Your thermostat probably opens around 195 so the 195-220 range is the "ideal" operating temperature. If the airflow driving around the city is sufficient to cool the radiator, your fan may not turn on. I know in the late fall/winter/early spring when the air temps are cooler, my Montana minivan's fans never kick on unless I idle for a looonnng time.
When you turn the AC on, you need to draw additional air through the condenser coils to cool the refridgerant. That's why it runs when the AC is on.