On Sat, 29 Apr 2017 08:35:23 -0500, dpb wrote:

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.


It's for a cottage that is available to a number of people. It has
electric heat, which is *supposed* to be set at 5 degrees above freezing
when the users leave. They are supposed to drain the water as well.

But sometime they don't set it, and sometimes they don't drain the water
system, and sometimes the power goes out.

What I want is a system that will open a valve to drain the system
whenever

a) the power goes out, or

b) the temp gets too close to freezing.

I can do a) with a relay or contactor (which will also cut power to the
pump) and a electrically operated valve, but for b) I need a switch that
will cut power to the relay.

Educating the users has not worked (twice, counting the number of times
pumps broke and pipes-had-to-be-replaced). A machine you only have to
educate once.