I finished the rear faceplate, and have the A/C hooked up and verified:

Unfortunately, when I plugged the controller (microcontroller + DAC + display) in, I let the magic smoke out.

It appears the problem was due to a faulty 7805 regulator which I had salvaged from who knows where. The regulator output 10v instead of 5v... which obviously didn't do so well for the AVR. The display has (luckily) appeared to survive (although I have only done some minimal testing with it, so there is still a chance that it is bad). I am unsure whether the DACs survived or not; I know that at least one channel on one of them is outputting the correct voltage, but without a working AVR I can't really set the voltage for any of the other ones.

My plan is to solder up yet another controller board, and this time test my regulators before I use them. Hopefully I will have time for that in the next few days.

Cheers