[jeff5may]

So what is your overall impression of the chinese temp controller? I mean, other than your desire for total control of all parameters (which may or may not be possible with the off-the-shelf Chinese unit), how does the unit track and/or learn or respond to its environment? I see it strayed or drifted a bit on you. I'm seriously considering using one to control some sort of heat pump monster in the near future. Regular heat pump thermostats are not that much more expensive, and some have lag and swing controls built in also. Probably not as wide-range as the Chinese unit, but then again the temp sensors don't drift either.

Some of your frustration may be built into the deep freeze itself. I'm sure the unit was built for lower ultimate temp, rather than rapid pulldown. With a cap tube setup, this means lower mass flow and suction pressure, regardless of ambient or box temp by design (longer cap tube). It may not be advantageous to try to limit your box temp/evap temp to prevent frost unless there is some kind of airflow inside the chamber.

With the teensy controlling things, you might be able to add more sensors and gain insight into the temps of everything, but with the stratification and lag (due to the lack of airflow) in box temps, I'm not sure it would do so much good. As temps get close to freezing, you may NEED to have frost to transfer enough energy out of the box. I guess it all depends on how short you want the cooling runs to cycle vs the inherent lag.