[Chrislong]

It depends on the car. A big torquey diesel will hardly be effected by it, but a weaker 1.2 1.4 petrol will be under more strain. I found my 1.4 Fiesta was effected by approx 10% by Aircon, but my 2.2 TDCI Mondeo isn't by anything I notice.

If you want it on, put it on, the difference it makes even at 10% can be also as much lost by an unserviced car, heavier right foot, poor clutch control or even sitting with tickover on when no need to.

You know the recharge thing? Kwik fit or who-ever say they'll recharge the aircon and make it work better or else its free, this is always the case as I am informed new cars aircon is never completely filled - hence always an improvement on a recharge/fill!