After 25 years of motoring i just recently bought my first ever brand new car (a wee treat to myself) now i've had cars in the past with air con but i remember reading somewhere that the air con should be used to lubricate the hoses in the compressor to stop them cracking and drying out,but how often should this be done........i think it was something like 10 min's but cant remember if thats per day/week or month.......?
one thing aircon is excellent for is making window condensation clearing more efficient. This is worth paying the extra fuel for when you have two big wet dogs.
Mine is permanantly on as it is a climate control system. It turns off at 5c to pevent freezing. It uses no petrol as my Octavia is a diesel!
I get about 45mgg around town.
extra fuel is minmium, it just talks it bit more power from the engine to run the pump, when you turn the aircon on especially when idling you can hear the engine note change as it struggles a bit, obviously the smaller the engine the more noticeable it is.