How to connect unused green wire at Argo switch relay to use as C-wire?

jckenny

Hello, I would like to install a smart thermostat for my hydronic heating system, but my green C-wire is not connected on my Argo ARM-3P switch relay:

https://imgur.com/a/nwwYIqv

I was hoping I can just connect it to somewhere on that Argo switching relay and have a working C-wire (for example in the upper right corner the red wire is connect to a "Common" terminal, can I also connect the green wire there and call it a day?). But from googling, it seems like people recommend installing Argo IR882 or a RIBUC1 but I wanted to see if you guys have any additional ideas. As a last resort I would probably consider getting one of those ac adapters for the nest that I can plug into an outlet.

Here's the manual for the Argo switching relay: https://argocontrols.com/sites/default/files/AD1-AD4 IOM.pdf

Thank you for taking a look

Jamie Hall

Yes, that terminal in the upper right corner is the Common connection from the 24 Vac transformer on the Argo. The other terminal there is the hot 24 Vac connection from that terminal. So... before you do anything else, what are the red and white wires shown connected there on your photo, which are labelled "to the boiler" connected to on the boiler? Without knowing that, you stand a good chance of shorting something...

jckenny

This is my rudimentary diagram of what happens to those upper right red and white wires: https://i.imgur.com/wDzyQwu.png

The red wire goes into this wire nut with the red wire from the guard dog low water cutoff along with the pink wire that goes into the Weil McLain WM Boiler Ignition Control Board 511-330-088 at R here: https://i.imgur.com/cyt5X6E.png

The white wire goes into this wire nut with the white wire from the guard dog low water cutoff along with the brown wire that goes into the control board here: https://i.imgur.com/Mo64p5V.png

The diagram of the control board is from page 38 of the boiler manual https://www.weil-mclain.com/sites/default/files/field-file/cgi-series-2-manual_1.pdf

Here are some additional pics of the wires https://imgur.com/a/1lhwvQS

EdTheHeaterMan

Wow. you got lucky. or the installer got lucky I should say. The R & W from the ARGO 24v R and Common should not be connected to the R and Common of the Weil McLain boiler control. If the wires get reversed somehow, the transformers will no longer be in sync creating a 24V parallel circuit. Reversing the R & W wires will create a 48V dead short and burn up some electronic parts.

Do this.

Remove the upper right wires that "Go to the boiler" and see if the system still operates properly. if that is the case, then do some tests... See if the thermostats from each zone operate the boiler. See if the green light on the GuardDog LWCO gets power. Removing the wire from the ARGO to the Wire nuts between the LWCO and the Boiler Control is unnecessary and should have no bearing on system operation.

EdTheHeaterMan

Once that is tested and you find a positive result, (= everything works without the above-mentioned wire) you can now connect the R wire from the thermostat to the T on the ARGO that has a small R next to it. The W from the thermostat gets connected to the T on the ARGO with a small w next to it. it appears that your connections are already that way, but double-check. This is important because the small R indicates that the T terminal with the small R is connected to R of the transformer in the ARGO. This connection is internal to the control board circuitry

Finally, you can now use the C on the Argo Control board for the green common wire to power the thermostat

EdTheHeaterMan

Suppose the system does not work with the above-mentioned wire removed... Then this means that the boiler transformer failed at some point in the past. In order to get you temporary heat, I would use the transformer in the ARGO to run the boiler until I could return and replace the Weil McLain transformer. If that is the case, then test the Weil Mclain Transformer to see if there is 24 V when 115 V is applied to the primary (B and W) wires. This should be easy to do by disconnecting the wire nuts where the ARGO was connected.

Let us know what you find.

Jamie Hall

At @EdTheHeaterMan 's got it -- and you did get lucky. In the meantime, while you try his experiments, don't connect that green wire to anything on the Argo. You could very easily fry either the Argo or the burner control or the LWCO or the thermostats -- or all at once.

jckenny

Thank you @EdTheHeaterMan @Jamie Hall

By the way, before I unplug the Red and White wires from the upper right of the argo, I noticed this on my boiler transformer and I just wanted to check with you guys that it's expected, there's two wires coming out of the boiler transformer just chilling there: https://i.imgur.com/5OH3wFa.png , is that normal?

Jamie Hall

Wonderful. No, it's not normal. It looks as though for one reason or another someone may have disconnected the boiler transformer and substituted the Argo transformer for it. But... to make certain, you will need to try the tests that @EdTheHeaterMan suggested.

The bottom line is that you want one, and only one, transformer feeding 24 Vac into the system.

jckenny

Ok, just tested by unscrewing the top right 2 wires from the argo, the LWCO light went out and the boiler is not responsive to any signals to turn on.

So I guess that means the boiler is using the transformer on the argo in a hacky setup huh. Would the best approach be to connect that boiler transformer back with the rest of the system? I do have a voltage meter on hand but I have no idea how to test if the boiler transformer is broken

(I could also just buy a new transformer of the same model for like $35 and replace it, but I still have no idea where should the wires go from the transformer. Do I just put the pink and brown output ones with the LWCO wire and the pink/brown wires currently on the control panel at the green circle here, and then plug the black and white input wires into the blue circle area here , while also disconnecting the red and white wires in the upper right of the argo?)

Jamie Hall

You know, I think I'd simply say OK... the boiler transformer is, for whatever reason, toast and the system works OK with the Argo transformer and go from there. The C terminal on the Argo should do fine.

Note that the Argo has a built in fuse on the 24 Vac side, so if you do overload it it should just shut down... you hope.

jckenny

Gotcha, yeah that sounds good, I think I'll call it, and use the Argo Common for the green wire. Thank you both for your help!