I did make a few more tweaks to the differential controller the other day. Mainly, I was getting some noise over the long run of the wire going to the kitchen sensor. So, I added a 10 uF capacitor near the controller to act as a buffer. This smoothed out the signal and everything seems to be working great. See the
thermal differential controller thread for more info.
I still need a nice sunny day to see if it kicks on though. The other day was nice and sunny, but it must have been too windy. As I saw, the attic only got up to about 65F yesterday.