Everything is airflow.. My mantra is "Charcoal always burns at the maximum volume for the given airflow."
If it's not hot enough, open the damper top. It's too hot, close it a bit.
If your fire went out and it was not an issue with the moisture content of the charcoal it did not have enough oxygen to burn. I'm guessing the top was too tight/closed and the exhaust was not getting out. For 235º the top is barely cracked, and it's easy to close it too much and kill your burn.. We've all done it. I usually put my hands near the damper top to feel for the hot air if there is no smoke to see. I drive my cooks from the damper top.. If it's not leaving the top, it's not getting in the lower draft door. The vacuum is from the hot air exiting.