I just got my WSM and Auberins Temp controller, I attempted to do a burn off and prepare for a nice long cook next week. I added one chimney of K Blue coal that sat in the chimney for 25 min. I added the coal to the smoker and closed the remaining two vents and left that top vent open. I added enough water to fill the coal 50% and set the controller for 250F. The temp rised fairly quickly and hit 277 for about 20 min and then dropped below 250. Once it dropped below 250 the fan kicked on at around 225-215, by then it was too late and it could only hold the temp at 179 for about 80 min. By then most of the coals were burnt out and the temp was slowly declining. What am I doing wrong?