5 wires? Compatible?

[Kim6]

 

 

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my current thermostat is an outdated Honeywell that runs on 2 batteries.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?

[Peter_fromAZ]

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. 

[Charles333]

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).

[Charles333]

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.

[Charles333]

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.

[Kim6]

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

I was confused about the wires myself…

[Kim6]

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.

[JohnsonMartinez]

no I fell down writing this