lol. Aircon on 1 should be fine. It's not worth the heat. Lowering your windows will reduce fuel economy even more because it will greatly affect the car's drag coefficient. If you want slightly better fuel consumption and power, you can do the following:
1) Remove the long pipe + resonator just before the airbox, it will allow the engine to breathe better. If you want it to suck cool air, get a flexible intake hose and direct it to the slot just behind the left side of the grill. You can see the slot below.
2) Do a coolant bypass so it doesn't run through the throttle body anymore, which will allow the throttle body to stay cool.
3) Replace your stock air filter with an aftermarket air filter. K&N filter number that fits our Swift is 33-2968. Hurricane/Ferrox filter number would be HS-0301. We have the same filter as on the Ertiga 1.4 petrol.