Question on offset smokers

I'm a new owner of a cheyenne. I start a fire with charcoal and the temp is 150-250 I have two temp gauges like a loaded whitcha they are in this range one is high one is low my digital thermeter on the grates is about 190 max... I have been only cooking with charcoal should I put fire wood on to cook with. I have been opening a closing the damper...PLEASE ADVISE WHAT TO DO TO BRING UP THE TEMP... To cook a small chicken I'm going on 3 hours and I have a temp of 155 F...
Mark
Mark