"unk" wrote in message
news
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.

I gave you several suppliers and search terms. Usually switches need
to close near freezing to turn on heat, except for refrigeration
thermostats which open when cold. However the fixed-setting
replacements I found had a wide tolerance, which is why I would use an
adjustable thermostat and test its setting, differential and
repeatability.

-jsw