Wet and warm weather can affect the draft so keep an eye on things and make sure that there is no moisture in the hopper (a sign of poor draft). If there is, you can increase the min a few numbers to make more heat go up the chimney. As far as causing red coals to go into the ash pan that is a factor of coal being able toburn completely. I'm not convince that maybe you are just seeing some peices that will not burn completely. A picture would help tremendously.
You can set the Coal-Trol on max and adjust it down until there are no red coals falling off the grate, also check and see how high the flames are. The main thing is don't give up, sometimes it takes a little while to figure out what is going on.