Wow! Those graphs make understanding the tuning parameters much easier, thanks! There's still the issue of PID control, regardless of tuning, after the overshoot it should come back on. Maybe the overshoot is taking so long, greater than the windowsize?, or something of that sort that is causing the PID logic to fail. Once it over shoots it takes a good 5min+ to cool down, in the image i had the coil/therm up against my wall AC unit on full.