topic Re: 5 wires? Compatible? in Nest Thermostats

5 wires? Compatible?

Kim6 — Thu, 11 Aug 2022 13:57:51 GMT

Hello, my new HVAC man recommended a nest ‘learning’ thermostat w/ sensors. (Sexy).
my current thermostat is an outdated Honeywell that runs on 2 batteries.

His partner went to install the Learning thermostat, and said it can’t be installed without a C wire. (makes sense).

Currently, I have 5 wires (which appear to be) labeled as:

W2, G, W, Y2, R.

I took a pic.

The (awesome) nest app provided a ‘diagram’ of where I can attach my current wires to the nest thermostat!
how exciting,

Except… my HVAC man said the nest doesn’t run on batteries and still can’t work without a C wire.
😞

So haven’t tried installing it yet.

Can anyone confirm this won’t work?

or explain it to me?

I understand I have no electricity to run a thermostat without C-wire,

but then I noticed the box of nest thermostat stating it doesn’t need a c wire? And works with 95% of homes.

second concern,

He said he “can add a C wire”

however, I’m concerned. Before I do this, is there a way to double check this will guarantee the nest learning thermostat will work for my home?

(I’m becoming tired of the “should have” and failures.. 😞 and past hvac cover ups by prior crew and more money being wasted)

Is this thermostat actually compatible?

Re: 5 wires? Compatible?

Peter_fromAZ — Thu, 11 Aug 2022 16:56:47 GMT

I am not an HVAC expert. (I hope an expert will reply to you.) But I installed 2 Nests in my home on 2 existing heat pumps. Both had a 'C' wire. The 5 ton unit worked fine with the 'C' wire hooked to its Nest, but the 2 ton unit refused work properly until I DETACHED the 'C' wire. After searching the Internet, I found others reported the same, but very rare condition. I think you can safely hook up the Nest as it guides you, trying the existing wiring, and test for functionality.

Re: 5 wires? Compatible?

Charles333 — Fri, 12 Aug 2022 01:20:09 GMT

Certainly a common is preferred. I would start by giving the current bundle at your thermostat a good tug. There is a chance there are more unused wires.

If not, it is true there is a fair chance it would be alright without one. Got a voltmeter? Measure the AC voltage between R and the other wires. You may well be getting a good enough ground return via the other wires. I think 24AC can be quite forgiving.

Your wires used are weird. Y2? That implies Heat Pump. But no O/B? - not good.

Do you have a Heat Pump?

What kind up main heating? One or two stage?

You really need to find where the wire bundle is going. It will be near furnace/air handler. That will tell all.

Re: 5 wires? Compatible?

Charles333 — Fri, 12 Aug 2022 01:26:24 GMT

Peter, the other end of the C wire must have been mis-wired. Usually the 24AC (R) and it's common (C) come directly from a 120VAC to 24AC transformer. Bringing R and C from the transform will work (unless the transformer is bad/overloaded).

Re: 5 wires? Compatible?

Charles333 — Fri, 12 Aug 2022 13:50:21 GMT

You most likely do not have a heat pump and the Y2 is for your air conditioner.

And yes, the Nest will be compatible once you get the C line sorted out.

Re: 5 wires? Compatible?

Kim6 — Sun, 14 Aug 2022 15:23:22 GMT

The new HVAC man said we have a two speed heat pump.

I was confused about the wires myself…

Re: 5 wires? Compatible?

Kim6 — Sun, 14 Aug 2022 15:29:36 GMT

Yes, 2 stage heat pump!

Im concerned about the wires..

The Honeywell thermostat was installed November 2021… by a prior hvac man (totally screwed us every way). He said it was new, he likely got it from a past job because it was filthy. He was supposed to do everthing, including the wiring, but I suppose he got lazy. (We had to replace all the ductwork he did as well by a different crew). Paid him for premium services and parts and got the lowest quality crap. I’m not surprised this was his cheap solution.

Re: 5 wires? Compatible?

JohnsonMartinez — Fri, 18 Nov 2022 18:21:25 GMT

no I fell down writing this