On Sat, 29 Apr 2017 12:08:18 -0400, "Jim Wilkins"
wrote:

"dpb" wrote in message
news
On 04/28/2017 11:33 PM, dpb wrote:
On 04/28/2017 10:15 PM, DoN. Nichols wrote:
...

How will the board continue to work without backup power?

...

That's the point; it doesn't need to.

To amplify, these boards retain their settings on power-off so if
use the NO contact and the "COOL" side so closes on TSetpoint, when
power comes back on the relay won't close to restore power to AC if
the temperature is below the turn-on setpoint.

Which use begs the question of why OP would leave the AC energized
once it's even remotely close to freezing, anyway...a solution
looking for a problem here.

--

I guessed that it was a DIY solar water heater. For a one-off home
project there are thermal switches in discarded refrigerators and air
conditioners that might be suitable. Some are open-on-rise and may
require a relay, perhaps a solid state one to avoid opening during the
pump's starting surge.

-jsw

If it's a solar water heater, then products like this with built in
freeze protection are readily available.
http://www.solarproject.co.uk/manual...structions.pdf

Under "frost protection" it seems to ignore drain down/back valves,
which are common in plain-water, uninsulated-collector setups.