Nest Power Connector Manual Testing

[graussofj]

I am trying to determine if the power connector I have is defective.  Here is what has happened:  I was trying to install a snow Nest thermostat in an old building at my church.  The original thermostat was a programmable with only two wires for heating, RED and White.  As per direction by the App, I installed a nest power connector, and it was not detected by the Nest thermostat.  I then checked wiring and everything was correct.  I also noticed that the thermostat wiring had been spliced somewhere between the furnace and the thermostat, and when I tested the wires for continuity, I found that the wires had been reversed when they were spliced.  I then reversed the wires to provide correct polarity, but still no power to the thermostat.  I then disconnected the thermostat wires at the power connector and checked voltages on the connector.  On the Thermostat side I get no voltage and should I be getting 24V?.  On the furnace side I get 24V C to R, 24V R to W, and 0V C to W.  My question is, was the power connector damaged by having the wires reversed to the thermostat, did the power connector go into some protection mode and shutdown, did the thermostat disable the power connector, and it needs to be reset?  Can the power connector disable itself and need to be reset, or is the power connector defective and I just need to replace it?  As I write this, I am home and have re-installed the old thermostat.  Please provide any guidance on my situation, and steps to take when I go back again to try to install the new thermostat again.  

[Houptee]

You are better off running a new 5 conductor thermostat cable to the Nest. They sell it in 50ft and 100ft rolls at big box stores, Then connect a real C wire and R and W.

Usually they will pull thru the wall pretty easy as long as they were never stapled to the studs but you can check by pulling up and down on the wire in the wall feel if its loose then attach new wire to the old and pull it thru the wall.

[graussofj]

Hi Hauptee,

Running a new wire is not an viable option.  I've used the C wire alternative on my home, but I have always had extra wires in the Thermostat cable, but not here.  Does anyone know the answers to my questions about the power connector and what voltages are supposed to be on the Thermostat wires coming out of it, or whether it needs to be reset or enabled or replaced?

[Houptee]

At the Nest if you remove the Red and White and put a voltmeter set to measure AC volts you should read 24-30 Volts AC.  The power connector provides a path to the C common side of transformer thru the White wire to simulate a C wire connected.

If you dont have any voltage on R and W at Nest something is wrong with the power connector.

[graussofj]

Hi Houptee,

Thanks for your input.  I did exactly what you said and there is no voltage across the R and W leads to the thermostat.  Do you have any Idea what the internal mechanism is inside the Power Connector?  Is there a latching mechanism that put the Power connector in a constant state of connecting the C wire to the White wire after the thermostat calls for heat that would cause you to read no voltage across the R and W wires when in that state?What I did not mention was that before I discovered the R and W wires were reversed, I had in inadvertently connected the power connector to a second conventional thermostat that was calling for heat and when I figured that out, I disconnected it and connected to to the Nest with the initial wires reversed in the Nest Thermostat.  I did'nt mention that because I read that the power connector will also work with a conventional thermostat without damage in the case that you remove a Nest Thermostat for maintenance reasons and replaced it with a conventional one without having to remove the Power connector.  Could it be that the when I measured across the R and W leads, the Power connector was still in the state of connecting the C to W lead and it needs to be reset somehow back to the calling for heat state?  Would a power test from the Nest thermostat fix that situation?

[graussofj]

Here is additional information on this problem.  The heating system has a "System 2000" energy manager to control the two zone valves on the system.  I had read earlier that if you needed a C wire that you would use terminal A2 on the system manager.  Well, I just assumed that I could hook up the power connector by connecting the C wire to A2 and R to T1 and W to the where the white wires were connected.  Looking again at the connections in diagrams shown on the System 2000 site, it appears that the white and red wires are reversed.  So I am really confused.  Can anyone tell me how I would connect a power connector to a system 2000 to make the Nest Snow thermostat work?

[Houptee]

I'm not familiar with that control.

You need to contact them and find out what terminal is R + power out and what terminal is C common.

They must have online documentation for the control and using it with any smart thermostats that all need a C wire.

There is no way to reset the power connector it is probably a transistor circuit inside but I never saw a schematic of the internal circuit. It basically lets current bleed thru to common on the white wire to keep Nest charged.

[graussofj]

Thanks for the info.  I searched for connecting a Nest thermostat to a System 2000 and found several ways to wiring it without a power connector.  They are described here:  https://energykinetics.com/wp-content/documents/display-manager/nest-power-sharing-wiring.pdf

I am going to try the 200 Ohm resistor option to see if that solves the problem.

[Houptee]

Did you have the Power connector hooked up like this:

3 wires set:

R to A1

C to A2

W to T (zone #)

And the 2 wires set:

R coming from Nest to R with the splicer

W coming from Nest to W with the splicer

[graussofj]

No, I put the W wire with other W wires on the A1 terminal and the R on the T1 terminal of the three wire set.  That is how the thermostats that I was replacing were wired (with the R wires going to the T terminals, and the W wires tied together on the A1 terminal), so I kept the same polarity.  Since I had the R and W wires reversed, maybe that Is why I did not get the 24V across the Thermostat wires on the power connector going to the thermostat.  Maybe, before I do the Resistor option, I should try the power connector again with the wires reversed as you suggested.

[Houptee]

You can't have multiple thermostats connected to one power connector only one thermostat.

The T# terminals on the control are for each thermostat.

W is the output from the thermostat it has 24v when the thermostat is calling for the heat to turn on. So only one white wire should be going to a T# terminal.

This is based on the wiring diagram document you posted.

[graussofj]

Hi Houptee,

Well, I have finally installed two nest Snow thermostats on the System 2000 Energy Manager using two nest power connectors.  I wired the power connectors with the W wire on the T terminals and the R wire on terminal A1.  The C wire was wired to the A2 Terminal just as you suggested.  I never tried the 200 ohm resistor method, because the documentation said it would only work with 3rd Generation thermostats, and I could not discern what Generation I had, so I went with the power connectors which appear to work with any generation. So, thanks very much for all your help!

[Jeran]

Thank you for helping out on this thread, Houptee!

Hey there graussofj,

I'm just checking up on this thread, and I'm glad to see Houptee was able to help you out! In that case, do you have any more questions or need any additional help?

Best regards,
Jeran

[Jenelyn_O]

Hi there,

Chiming in — I wanted to follow up and see if you still need help. Please let me know if you're still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

Thanks @Jeran and @Houptee,

Best,

Jenelyn

[Jenelyn_O]

Hi graussofj,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this thread in 24 hours.

Best,

Jenelyn