Citroen C3

[Calmate]

Please excuse my ignorance, but can anyone give me any advice on the Citroen C3's heating/ air con system? I just bought this vehicle from a national dealer but it was a surreal experience, due to lockdown. I did not meet the salesperson until the click and collect stage.
Now the heating system seems baffling to me. I have experienced the air con in previous cars to eat up petrol, so I didn't use air con much. In this C3 (2017 model) the heater and air con seem to be combined, I've not had the car a week and the on the first journey I noticed the air con was on auto, and the petrol tank was nearly empty after 40 miles, and I had filled up with £30 of petrol.

Didn't the car come with a manual? If not Google finds carmanuals2.com/citroen/c3-2017-owner-s-manual-103039. I have not checked the link.

Modern air con shouldn't have that big an impact on fuel consumption. Our Grand C-Max is bigger and heavier than a C3 and will still get 35 to 40 mpg, even though the air con is always on.

Thankyou, no there was no manual with this car, and the M.O.T. they gave me was for another C3 which a customer has reserved ! I had to take the M.O.T back to dealership. The salesman told me to go on line for manual app, but I am not a techie and have no printer on laptop, I usually get printing done at a local library, but they are all still closed.
Will look the manual up on line though, thankyou.

Aircon will make little difference to the fuel consumption of a modern vehicle. If it genuinely used £30 of fuel to do 40 miles then it’s doing 7mpg and is seriously broken. The only way to get an accurate figure is to brim the tank, reset the trip counter zero or note the mileage, use the tank, brim it again and calculate the fuel consumption.

Good advice, thankyou will make a note of mileage when I next fill up with fuel and calculate what the car is using.
Thankyou both xx