Nest Learning Thermostat Upgrade Help w/ EWC-ST-2E

[Killtrend]

Edit: Job complete and thread closed. Super easy. Highly recommend doing it yourself. EWC is super fast and helpful to boot.

Hi all. First time homeowner here who really doesn’t want to pay the $800 I was quoted to fix this.

So I have an old pair of basic thermostats I want to upgrade to Google Nest Learning Thermostats. I was all good to do it solo after the HVAC guy said it was compatible so I bought 2 and waited. When they arrived I tried to install and I noticed they had a blue wire but in the wrong location and a brown wire in the “o” spot. He internet says this is a heat pump and I definitely don’t have that. The HVAC guy messages back and says it’s NOT compatible now and I need to run a new wire, get a new panel, and pay $800 for him to do it. lol, no thanks. Hopefully you guys can help. It appears the previous homeowner had the following setup:

-2 Honeywell Home basic Thermostats
-“Hi Boy” oil heat forced air furnace
-Rheem AC unit
-Ultra-Zone Control System model EWC-ST-2E
-A random box (dampers?) thats called “trol-temp”
-The panel controls 2 zones. Main floor is the “master” and the 2nd floor is the “slave” (turns off regardless of temp if bottom floor temp is satisfied). Top seems to be wired for heat only as well. Not ideal but at this point I don’t care.
-The master thermostat has 6 wires. The slave has 3.

Wiring is as follows (also see pictures):

Main Thermostat:

W - White
Y - Yellow
G - Green
O - Brown
Rc - Red
R - Empty
B - Blue
C - Empty

2nd Floor Thermostat:

Rc - Red
R - Empty
Y - Green
C - Empty
W - White
G - Empty

See pics. I also added pics of the AC and Furnace in case you need that. What do you guys think?

[Killtrend]

Main post seems to only show 3 pics on my post through mobile so I added the rest here:

[Steven W.]

If you are looking for a Thermostat for the master zone on your ST-2E / ST-3E 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-2/3E Boards program them to Heat/Cool not Heat Pump. The Heat Pump setting will not work for the ST-2/3E 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

You will need to update your board to a NCM 300

You can get that board from:
www.ewcestore.com
www.supplyhouse.com

[Killtrend]

Alright. NCM300 it is. I’ll look into that today.

Will this new board allow me to automate the “manual changeover” you mentioned? It appears my master has both heat and ac was working with no changeover required currently (although I assume the slave will need changeover with only 3 wires. Can I just run a new 6 wire to it with this new model?)

Also, what do I do with the O and B wire on my thermostats after I install the new panel? B (blue) move to common? If so, where do I put the brown from the O since the nest doesnt show an O?

I’m probably asking questions that will be obvious once I’m holding the new panel, sorry!

[Steven W.]

The "O" and "B" wires are now just spare wires. Yes the NCM will automatically change over and every zone can call for heat and cool when ever.

[Killtrend]

Both spare? I don’t need a common now for the two nest learning thermostats? If not I’ll just tie them off and tuck them.

I assume everything else is 1:1 judging by some quick googling although the wiring on “system” and “24dc transformer” is labeled different.

In system: I have R (to your RH or RC?) and W (to your W1 and W2?)

My 24v Transformer is also 1 (red wire) and 2 (white wire) to the new panel’s schematic calling it R and C. Would I put my white in C in this case and Red in R or leave it how my picture shows which would swap them?

Thanks for the help, Steve. I ordered the panel. Just gotta wait a couple days.

[Steven W.]

Yes you will need a "C" wire for both nest stat's

"R" to "RC or "RH" there is a jumper wire built into the board so it does not matter where you put the "R"

"W" to "W1"

Yes Red to "R" and White to "C"

[Killtrend]

Nice. Seems pretty simple. I’ll steal a C wire from somewhere for the bottom thermostat. Probably have to run a whole new cable upstairs as that’s only 3.

I came across this YouTube video of a guy doing exactly what I have to do, literally, but he said I shouldn’t put two wires in the red RC/RH slots due to compressor and Heat running together but it seems my system (see original pic) has two wires in that red slot already (bottom left of the panel).

@ 6:44
https://youtu.be/pqDAymD3c-A

If I follow that YouTube video where he talked to some guy named John at your company, I’d have to stick one of those red wires in Y. Thoughts on that doubled up red wire at the bottom left of my panel?

[Steven W.]

That is a good video to follow. I included those document's for you.

[Killtrend]

Update: Done. This was a SUPER easy install. Thanks Steve!

Had two hiccups that I worked through. One was confusion on how long it took they system to switch from heat to cool to test. Solved this problem by reading the manuals “common issues” and hitting “reset” to skip the timer. The other was confirming the wiring on a mislabeled 24v transformer which Steve answered when I called up. Couldn’t be happier with the swap. Took probably 2 hours from start to finish but most of that time was spent labeling my old wires, cleaning up routing, and such. If you’ve got a super clean system and have even a basic understanding of simple wiring, this job can be done within an hour. The only tools *required* are a terminal screwdriver, whatever you’re using to mount the box (probably self tapping screws or wood screws), some labels or masking tape with a felt tip marker, and basic wire strippers. Be careful when doing the punch outs! There’s a reason they put a “STOP” insert in there. Cut around the edge of the hole with a folding knife (or whatever) by plunging it over and over in the indent (carefully so you don’t cut yourself) and then pop it out with a wiggle.

I didn’t install the SAS that came with it because I’m not entirely sure where to install it on my system (the manual tells me the plenum, but I don’t know what or where that is) but it’s optional anyway. If I figure out where that goes that should be a 5 minute job (drill two mounting holes, drill a hole for the sensor, run a 2 conductor wire to the labeled terminals and bob’s your uncle). Pics attached of my finished system. Reference the first post for a comparison if you found this post through Google. Ignore zone 2 in the pic; I only ran zone 1 to a new Nest and left my legacy second floor thermostat alone. Gotta run a new 5 conductor for my other Nest tomorrow. Easy stuff, I’m just lazy right now.

My only gripe is that I can’t seem to get the system to stop obeying the master/slave dynamic. If I’m upstairs all day, and I want heat, I don’t want the bottom thermostat telling me to essentially kick rocks.