--- In Crestron@..., "marselle001" <marselle001@...> wrote:
in the old a/c system analog thermostat,analog thermostat (thier is
no
+24 v -24 volt )
actually u can use the cnet voltage in this case also , i tryed this
methode and its working perfectly.
You're connecting your cresnet ground line to one side of your furnace
control wiring?
The last thing in the universe you should to to a TSTAT is connect
Cresnet anywhere directly to your furnace. Regardless of brand.
Anything with a compressor in it (AC or heat pump) relies on the
thermostat to provide a delay timer after the last demand to protect
the compressor from rotor lockup. If you have your Cresnet power on a
UPS, the thermostat won't be able to sense a power interruption.
Secondly, in the US, most hvac systems rely on 18-24v AC transformers
to to interface to the thermostat. Furnaces don't have very good noise
and surge protection. Connecting Cresnet ground to one side of an AC
transformer is asking for intermittent problems.
The ONLY way to safely and reliably mitigate not enough wires in the
thermostat cable is to use add a simple 18-24v ac transformer, plugged
into a normal AC outlet, supplying ac between C and Rs, and hope that
when there is a power failure, this transformer goes down too.
