This week??
Just driven for 55 mins with air-con on (as always!) temp control set max cold... Upon return to base, using two 12" Gallenkamp Griffin mercury thermometers I found :-
Out side of car shaded free air, temperature of 22°C ... Unshaded 25°C
Air discharge at face vent in car 8°C in car humidity 50%.
7yrs and near 70k miles past the car salesman said, "It has been my experience that having the air-con 'switched on' all times gives least system problems .. at a minimal cost.."
I have followed that advice winter / summer. My diy a/c service comprised one pollen filter vacuuming and a whole can of Dettol Disinfectant spray discharged throughout the ducting and airwashed internal paraphernalia a year or so ago -- I am happy with the performance of the air-con... No annoying, lingering smells, can just whiff the Dettol 'Spring Waterfall' on occasion, even now.
Fuel cost of running air-con approx £488 or £0.19 per day. @ 2 mpg
Cheap as chips !! ... and that was geeky !