Yes, we had a car in which we rarely used the air con and it eventually seized up and wouldn't work. The garage told us this can happen if you don't use it regularly. Then we discovered how efficient it was at de-misting and keeping the windscreen clear in cold, damp weather , so now I use it often, throughout the year, although only for as long as needed. I doubt whether the difference in fuel consumption is significant - my car is already low on emissions and petrol use. As someone said earlier, opening the windows probably affects fuel consumption as much, by making the car less aerodynamic.
It's easy to get hung up on small things like this. Cutting out a few car journeys and taking the bus would do more to save the planet than driving around in a car that's hot and stuffy, or damp and misty, in the hope of saving fuel.