Not really as you can use the A/c on hot or cold. I usually have mine set at 25 and it warms up pretty quick tbh.
I have mine set on 32 without the AC on, and fully on front windscreen when its fogged up... that's correct right?
If you want to clear the windscreen quicker you'd be better off doing what your doing but with the A/c on imo. Will clear it much quicker.