I just mean when I shut the damper down. That's usually a few hours into the smoke, (usually doing sausage or cure products in my freezer conversion). I have a lot of friends that attempt sausage making ask me how long and hot to smoke. This is really different depending on the sausage being made. The general schedule I tell them is: 1) Place into smoker preheated to about 130 deg. for about an hour or so with dampers open to allow the surface to dry. 2) Raise the temp to 150, close down dampers partially, and start smoke. 3) After another hour or so, raise the temp to about 170, continue smoke for about 4-5 hours, dampers nearly shut. 4) Continue holding at this temp til an internal temp of about 152 is reached (I go to 155 on my test sticks, just to be sure). Additional smoke is optional depending on size of links and your taste.
This is just a generalization and obviously can be varied from, but I've found it works well for most things. It is basically gleaned from Ryteks book, although nearly every recipe has a different smoke schedule. The main thing I have found after 15 years of sausage making is to not rush it, and don't get impatient and crank your temps up too high. You will only render out fat, shrivel the sausage, and get the burnt fat smoke smell and flavor, not a nice wood smoke.
Are your hot plates staying redhot throughout the smoke? I'd have the entire floor of the upper cabinet opened up to the lower. Get a jigsaw and cut it out., then some type of heat deflector slightly above it (perforated sheetmetal or some such). The dimmer makes me nervous, I'd ditch it for now, especially since the problem is that you are not reaching temps, not keeping them down.