Connecting a Nest Learning Thermostat to EWC-ST-2D

[jamesr]

I am trying to install a Nest Learning Thermostat (3rd Gen) to my 22 year old EWC-ST-2D. The Nest has a single O/B wire and the Ultra-Zone has both a Blue and Orange wire.

1) Is the Nest Learning Thermostat compatible with the Ultra-Zone Controller(EWC-ST-2D) Zone 1?
2) If so, how should the separate Blue and Orange wires be connected to the Nest (without the use of a manual switch e.g., MCS-DXB).

Thanks

[Steven W.]

Nest thermostats will not work with the ST-2D

There is no WIFI stat's out there that will work will the ST Boards.

If you are looking for a Thermostat for the master zone on your ST-2D / ST-3D zone boards here is a list of Thermostats that have the separate "O" and "B" connections that you are going to need for the master zone. Remember the ST series boards are master/slave (Winter/Summer manual changeover) so you are going to need these two connections on your zone 1 thermostat for your board to work correctly.

FYI
When you are programming the EWT-601-2 and EWT-725 Thermostats for the ST-2/3D Boards program them to Heat/Cool not Heat Pump. The Heat Pump setting will not work for the ST-2/3D Boards. There are NO WIFI thermostat's that will work with the ST boards.


EWC Thermostats
EWT-601-2 – None Programmable
EWT-725 - Programmable



PRO 1 Thermostats
T601-2 – None Programmable
T725 - Programmable

If you are dead set on using the Nest stat or any WIFI stat then you will need to upgrade your board to a NCM 300

[jamesr]

Hi -

It was recommended from my last post that I upgrade my existing EWC-ST-2D board to an NCM-300 if I want to use a Nest Learning Thermostat. Looking at my existing board, on the System Terminal Block, I have a red wire and a yellow wire going into the same yellow terminal (See photo). The upgrade documentation does not address this situation... so how should I wire these two wires on the NCM-300?

[Steven W.]

I don't see any pictures that show me those two wires. Can you email them to me?

Thank you
Steven R. Weisneck

sweisneck@ewccontrols.com