[Synchronicity]

Just wondering, if I'm going down a long hill and not pressing the accelerator pedal, it won't hurt mileage to turn the A/C on will it?

I routinely travel down some pretty long grades between 5 & 10% gradient here on the island of Tenerife. For a 500m /1500 ft hill, this equates to between 5 & 10km of continuous downhill driving. For the 5% grades I often coast in neutral and I can maintain my speed (75mph or 120km/hr) with the engine at idle. Other steeper descents it is better to do in gear as otherwise the brakes can overheat. So the engine revs are there but you're not using any fuel (apart from that used to make the engine idle I suppose) since you aren't pressing the accelerator pedal...

I'm wondering: does the air conditioning run from the alternator or it's own drive belt...?

I've been switching on the aircon on the downhill sections and turning it off for long uphills. I'm guessing this will improve my fuel economy? It seems that this is the only way of recouping or regenerating some otherwise lost energy when driving downhill...

For those that are wondering, outside temp in the Summer ranges between 20 & 30°C and my passsenger compartment stays cool for up to 5 or 10 minutes afterwards as I've had it fully insulated.