Recently purchased by Summit Charcoal. Loaded it per manual instructions for a 8-10 hour smoking session. After initially overshooting smoking range to 280F(on built in temp gauge and wireless probe system), eventually settled down to 230-240 for about hour and a half or two hours with bottom damper just to left of the smoke symbol dot and top damper at half open. But then temps started to plummet over one to two hours getting to 205 despite moving bottom damper a centimeter to right and top damper to full open and cleaning ash with the built in system. At 205 I moved the bottom damper to the fully open "grill" position. Temps eventually started rising again, I moved vent arm back to smoking position once in smoke range, temp now steady at 279. Obviously higher than I want. Main question, can you speculate why my temps plummeted? It's as if charcoal was oxygen deprived but I hadn't moved vent arm from close to smoking position. Can enough ash fall through grates to start to cover the vents? I have verified that the positions on the vent arm match the positions of the actual blades in the ashcleaning system. Ambient temps are warm, in the 80-90s, grill is in sun part of the time. Kingford blue bag charcoal with four chunks hickory.