(Nest Thermostat) HVAC Wiring Questions

[GlockSpock]

I decided to replace my older "Dico" thermostat with the "Nest" Thermostat. It's designed by one of the designers of the original iPod. It is pretty cool, integrates with mobile apps, etc. Supposedly super easy installation, which is was, however I always seem to be the one whom has a complicated setup when most people seem to have a simple one. Let me first state that it may be a dual fuel system, meaning gas or heat pump. However, we do not have the gas connected. It also *may simply mean that it is a heat pump and auxiliary/emergency heat.
 
I do not know much about HVAC, a buddy of mine knows quite a bit, we think we wired it correctly. It does spit out cool air when cooling, and it does spit out warm air when warming, so it is working. However, and perhaps it is simply because I am messing with it more and thinking about it constantly, but it *seems I've noticed the following:

• Takes longer to cool
• Perhaps the sensor is off a few degrees

I am going to get another thermometer to verify the heat sensor to see how accurate it is. And as far as taking longer to cool, perhaps not, but I just seem to think that. Anyways, here is the reason for this thread. Here is the wiring:
 
Here was the wiring setup in my old thermostat:
 


Here is the wiring for the Nest 2.0:



Here is how the Nest 2.0 *thinks it is wired:



What do you all think?

[glock55]

Thermostat wire color codes explained.
Please note. Not all installers use the proper color codes when they install or replace equipment. It may be necessary go go to the furnace or outdoor unit to verify what wires are for what purpose. Also be sure there are no splices in the wire that could change the wire colors between components.
 

• R (red) or Rh (Red heat) 24 volts from equipment.
• Rc (Red cooling) 24 volts from transformer in cooling equipment.
• Note: If only furnace has a transformer and cooling equipment does not jumper Rc and Rh.
• W (White) sends 24 volts to furnace control to start the heating cycle.
• W2 (no standardized wire color, usually whatever wire color is available) controls second stage heat.
• Note: W2 is most often used for heat pumps to control what is called emegency heat or Auxillary heat, and most often will use the white wire.
• Y (yellow) often (blue) is used, controls cooling unit (outdoor condensing unit) also is used for heat pump heat.
• Y2 (no standardized wire color, usually whatever wire color is available) controls second stage cooling.
• G (Green) controls the fan "on" operation of the furnace/air handler. Also often is used to start the blower for many electric furnaces.
• C (common) most often brown but can also be black or other color available to installer.
• O (orange) Energizes heat pump reversing valve for cooling (Trane and most other brands).
• B (Blue) Energizes heat pump reversing valve for heating (Rheem, Ruud and Weatherking).

perhaps this will help

 

have you been to the nest website , looks like they have all the tools to get you going there. did you check the compatibility guide?

Edited September 3, 2013 by glock55

[Guest 6.8 AR]

That's a better answer than I was fixing to give. :D

[TerryW]

I installed a Nest on an older home with an older HVAC system and was having loads of trouble. Ended up calling Nest tech support and the Nest techs couldn't figure it out either. They ended up sending a HVAC Nest knowledgeable tech out to set it up. I bought another one and it went in silky smooth. Edited September 4, 2013 by TerryW

[GlockSpock]

I installed a Nest on an older home with an older HVAC system and was having loads of trouble. Ended up calling Nest tech support and the Nest techs couldn't figure it out either. They ended up sending a HVAC Nest knowledgeable tech out to set it up. I bought another one and it went in silky smooth.

Another one being another Nest or another thermostat altogether? Also, what sort of issues were you having? Like I said...it hear and cools when I ask it to, maybe I am jus overthinking it but it seems odd.


Sent from my iPhone using Tapatalk - now Free

[Guest Cazador]

By looking at the wiring on the original T-Stat you will need to put a jumper  between Rc and Rh also on the original stat the black wire is used for an emergency heat setting. Which is used when your outdoor unit fails to run normally during heating. You can manually switch your t-stat to emergency heat which will the heat pump run on the electric heaters only. In your case I would imagine the original installer would have wired it to run the gas furnace, that you do not have gas hooked to. I am not sure what the terminal with the star is used for on the nest t-stat, where you have installed the black wire. 

Your original T-stat

R- 24 volt power  red wire

C- 24 volt common   blue wire    reading with a volt meter across these should read between 24 and 28 volts a/c

O/B- reversing valve   orange wire    O if your valve is energized in the cooling mode, B if it's energized in the heat mode

G- indoor fan    green wire

W2- second stage of heat   white or pink wire,   

E- emergency heat    black wire , this wire is connected to the same place as the W2[white or pink] on the indoor unit.

Y- compressor contactor relay    yellow wire

The Dico stat works like this... [ if the reversing valve is energized in cooling ] when the stat is set in cooling mode the O terminal energizes the reversing valve coil when the room temperature increases by 2 degrees above set point the Y terminal is energized turning the outdoor unit on. In the heat mode when the temp drops the Y terminal is energized turning on the outdoor but the reversing valve is not energized so you are basically cooling the outdoors in the heat mode. In both modes the G terminal is energized bringing on the indoor fan when a call is made.   Now the tricky part because you have disabled it due to not having gas supplied to the dual fuel. In the heat mode if the room temperature continues to fall another 2 degrees the stat will energized w2. If temp is set to 70 in heat the first stage [ heat pump] will come on at 68 degrees and the second stage [ electric strip or gas ] will come on at 66 degrees. The E terminal is only energized when you set the heat mode to emergency heat. The stat will by-pass the first stage of heat and energize the second stage [ electric strip or gas ] only.  This is where I am not sure what the star terminal is on the Nest stat.

[Guest Cazador]

Very few heat pumps energize the reversing valve in heating mode. The  Rheem / Ruud did for many years then they put out several models that were switched in the cooling mode.   

[Guest 6.8 AR]

I'd like to hear from you about how much you think this thermostat saves and functions in the future. At $249, it seems

pricey. Being able to use the "airwave" and "away" function is appealing, though. The remote app is only remotely

appealing to me.

[GlockSpock]

By looking at the wiring on the original T-Stat you will need to put a jumper  between Rc and Rh also on the original stat the black wire is used for an emergency heat setting. Which is used when your outdoor unit fails to run normally during heating. You can manually switch your t-stat to emergency heat which will the heat pump run on the electric heaters only. In your case I would imagine the original installer would have wired it to run the gas furnace, that you do not have gas hooked to. I am not sure what the terminal with the star is used for on the nest t-stat, where you have installed the black wire. 
Your original T-stat
R- 24 volt power  red wire
C- 24 volt common   blue wire    reading with a volt meter across these should read between 24 and 28 volts a/c
O/B- reversing valve   orange wire    O if your valve is energized in the cooling mode, B if it's energized in the heat mode
G- indoor fan    green wire
W2- second stage of heat   white or pink wire,   
E- emergency heat    black wire , this wire is connected to the same place as the W2[white or pink] on the indoor unit.
Y- compressor contactor relay    yellow wire
The Dico stat works like this... [ if the reversing valve is energized in cooling ] when the stat is set in cooling mode the O terminal energizes the reversing valve coil when the room temperature increases by 2 degrees above set point the Y terminal is energized turning the outdoor unit on. In the heat mode when the temp drops the Y terminal is energized turning on the outdoor but the reversing valve is not energized so you are basically cooling the outdoors in the heat mode. In both modes the G terminal is energized bringing on the indoor fan when a call is made.   Now the tricky part because you have disabled it due to not having gas supplied to the dual fuel. In the heat mode if the room temperature continues to fall another 2 degrees the stat will energized w2. If temp is set to 70 in heat the first stage [ heat pump] will come on at 68 degrees and the second stage [ electric strip or gas ] will come on at 66 degrees. The E terminal is only energized when you set the heat mode to emergency heat. The stat will by-pass the first stage of heat and energize the second stage [ electric strip or gas ] only.  This is where I am not sure what the star terminal is on the Nest stat.

Here is a snap of the manual:



(Emphasis added my me)
The * is, I suppose, a multi-use input by which it is accepting my "E" wire. So does that mean, I suppose, that the only other possible issue is the possibility of a needed jumper? I think I remember reading somewhere that either jumpers are not needed or not supported. I am looking for that right now.

EDIT: Found it. Documentation suggests that an R wire can go into either Rc or Rh, and Nest does not need a jumper between the two. So what are your updated thoughts and input? Edited September 4, 2013 by CZ9MM

[GlockSpock]

I'd like to hear from you about how much you think this thermostat saves and functions in the future. At $249, it seems
pricey. Being able to use the "airwave" and "away" function is appealing, though. The remote app is only remotely
appealing to me.

Well, it will be pretty hard to give an exact number, but I will attempt to update this thread with as many statistics as possible and then allow you to draw your own conclusion based upon those statistics. Ultimately, I believe it would be up to the user as to how much they save. I just programmed this schedule in via my computer, it's easy peasy! Everyday at 1AM, 82F, Everyday at 6:45, 78F, Everyday at 5PM, 78F. I think that perhaps that schedule means less that it should because of the auto away function. However, it's just a starting point and we'll see how it works. Honestly, the other thermostat was programmable but I never fooled with it because I never took the initiative to do so. Keep in mind that you are also paying quite a pretty penny for the fact that it was created by Mr. iPod Engineer. Now, it does indeed look great and turning the dial to set the temperature and other things make you feel like you are turning the dial on a high end safe. I for one love the idea of the mobile app because it will allow for me to keep the house a bit more efficient whenever I am not home but also allow me to set that comfort level if I know I am going to get home early. So we'll see. There is a lot of information available on their website. They claim an average savings of 19.5%. If I reached that, I'd be more than thrilled. Claiming the highest reported savings at 36.1%. Honestly, 10% savings would save me around $15 a month, so a year and a half it'd pay for itself. Considering that I wanted the Nest also for the "smart" features, I'll consider payoff a bit earlier. If it goes above 10% energy savings, that's even better. I will try and get a spreadsheet of energy usage per month over the previous year and then start comparing it to once I installed the Nest. Hard to say, but I'll see what I can come up with.

[glock55]

went to the nest sight appears your thermostat is compatible with a gen 2 nest thermostat. according to the video and walk through it appears that the wire you have at w2 should be located at w1.that is the only problem I could see.

[Guest 6.8 AR]

Hell, the programmable thermostat I have had a manual printed in four languages and they hid the English version.

I can get it to hold a temperature, but that's about it.

 

I would be curious how you think you're gaining. Just for some kind of justification for spending on a new thermostat.

Thanks!

[2.ooohhh]

Hell, the programmable thermostat I have had a manual printed in four languages and they hid the English version.

I can get it to hold a temperature, but that's about it.

 

I would be curious how you think you're gaining. Just for some kind of justification for spending on a new thermostat.

Thanks!

I did the math a year after we got ours and figured out that and save about $75- $100 a month in the hottest and coldest months of the year, moderate months energy expense is about the same. The pair of nests installed have certainly paid for themselves in the year we've had them. Our second Nest controls our baseboard heaters and a window ac unit in an addition and saves us the most in the winter while the main nest controls the rest of the home's HVAC which helps dramatically in the summer.

 

If your a little creative and handy with circuits they can control a lot more than Nest lets on on the site.(Likely b/c they don't want to support homegrown setups) One bit that took me a while to source for the baseboards was a mechanical relay for the line voltage that had a built in transformer to supply the nest with power. (previously had a line voltage thermostat)

 

 

For anyone who may be looking-

RC840T-240

[Guest Lester Weevils]

I have a $30 programmable thermostat that isn't hard to program and seems to work fine at what it does. The LCD is kinda low-contrast and I have to shine a headlamp on it to see it good enough to program.

 

Didn't realize the nest is so spensive. Old dad got one a few months ago, but his main motivation is that sometimes he feels too hot and sometimes too cold, and he has to work a lot to get up and walk to the thermostat every time he wants to change temp, so with the nest he can sit in his chair and micro-diddle the temp all day to his hearts content with his laptop or smartphone.

[jcj]

Not sure how to help with your wiring issue, but good choice on the Nest. Yes, they're expensive. I have the Gen1 model that I purchased at discount when the v2 came out.  The monthly "energy usage" reports are fascinating and you can see the cycle time of your heat or air down to the 15 minute interval for the entire month using the web tools.  The "auto away" feature is nice as well since it "learns" when you're home (or not) and adjusts the thermostat accordingly when you are away.

 

I replaced a honeywell programmable thermostat with the Nest. The savings are there even though I thought I had the Honeywell t-stat programmed for energy-conserving temps.  The Nest is just better at it I suppose.

 

Nest tech support is also great if you need them. 

[Guest Cazador]

Here is a snap of the manual:



(Emphasis added my me)
The * is, I suppose, a multi-use input by which it is accepting my "E" wire. So does that mean, I suppose, that the only other possible issue is the possibility of a needed jumper? I think I remember reading somewhere that either jumpers are not needed or not supported. I am looking for that right now.

EDIT: Found it. Documentation suggests that an R wire can go into either Rc or Rh, and Nest does not need a jumper between the two. So what are your updated thoughts and input?

 

The different uses of the star terminal suggests that during programing or set up of the t-stat you must select how it is to be used. on the Dico stat it was being used to operate emergency heat function.

I would suggest getting gas supplied to your system for it to operate properly once the temperature [outside ] drops below 35 degrees. If the directions state that no jumper is required and it actually operates the system in heat mode then you are good to go. T-stats with separate Rh and Rc terminals can control units that have a voltage reducing transformer in the heating system and a second one in the cooling system. Any system that I have installed with this set up I removed one of the transformers and wired the system to operate on one transformer. Doing this keeps the chances of crossing  voltage polarities [Basically causing a dead short in the low voltage ] to a minimum.

[Guest 6.8 AR]

I did the math a year after we got ours and figured out that and save about $75- $100 a month in the hottest and coldest months of the year, moderate months energy expense is about the same. The pair of nests installed have certainly paid for themselves in the year we've had them. Our second Nest controls our baseboard heaters and a window ac unit in an addition and saves us the most in the winter while the main nest controls the rest of the home's HVAC which helps dramatically in the summer.

 

If your a little creative and handy with circuits they can control a lot more than Nest lets on on the site.(Likely b/c they don't want to support homegrown setups) One bit that took me a while to source for the baseboards was a mechanical relay for the line voltage that had a built in transformer to supply the nest with power. (previously had a line voltage thermostat)

 

 

For anyone who may be looking-

RC840T-240

Well, that's enough to pay for itself, assuming house conditions are similar. My house is one of those "Big and Tall" ones in town. Ducted to heat and

cool close to 5000 sq.ft. Controlling another feature sounds good, like an attic fan added to it. I may be getting one of those things. Nice to know,

thanks.

[GlockSpock]

Here is a snap of the manual:



(Emphasis added my me)
The * is, I suppose, a multi-use input by which it is accepting my "E" wire. So does that mean, I suppose, that the only other possible issue is the possibility of a needed jumper? I think I remember reading somewhere that either jumpers are not needed or not supported. I am looking for that right now.

EDIT: Found it. Documentation suggests that an R wire can go into either Rc or Rh, and Nest does not need a jumper between the two. So what are your updated thoughts and input?
 
The different uses of the star terminal suggests that during programing or set up of the t-stat you must select how it is to be used. on the Dico stat it was being used to operate emergency heat function.
I would suggest getting gas supplied to your system for it to operate properly once the temperature [outside ] drops below 35 degrees. If the directions state that no jumper is required and it actually operates the system in heat mode then you are good to go. T-stats with separate Rh and Rc terminals can control units that have a voltage reducing transformer in the heating system and a second one in the cooling system. Any system that I have installed with this set up I removed one of the transformers and wired the system to operate on one transformer. Doing this keeps the chances of crossing  voltage polarities [Basically causing a dead short in the low voltage ] to a minimum.

Ok, I entered into the settings and setup the * to use it for the Emergency heat. I also found a setting that asks whether I have an O or a B wire. It states that the O wire is more common. I selected "I don't know". How do I find that out? And am I correct in figuring out that the W2/Aux controls the gas?

[GlockSpock]

Also, here is the way the Nest interprets the wires:



And of course here is how it is actually wired:
 

[GlockSpock]

Ok, I think I figured out that I have an O wire, or else it would be blowing warm air when cooling and cool are when warming. Correct?

[Guest Cazador]

you are correct. It would do the opposite of setting.  if it's not a Rheem or Ruud it is 99% of the time an O. Meaning the reversing valve is energized in cooling mode.

 

The W2/ AUX will control the gas in this configuration.

 

The way you have it wired in last pic looks good by their terminal designation. If the Rh and Rc do not need a jumper. There must be something in set up configuration that allows it to internally jumper these two.

[GlockSpock]

you are correct. It would do the opposite of setting.  if it's not a Rheem or Ruud it is 99% of the time an O. Meaning the reversing valve is energized in cooling mode.

 

The W2/ AUX will control the gas in this configuration.

 

The way you have it wired in last pic looks good by their terminal designation. If the Rh and Rc do not need a jumper. There must be something in set up configuration that allows it to internally jumper these two.

 

I don't believe Rh and Rc need a jumper. I'll take a photo tonight of the manual, it says if your old thermostat had a jumper not to worry about it, that an R wire can be plugged in to either and I suppose it just knows to take current from either. In fact, I'd bet that there is possibly a built in jumper between Rh and Rc, however that's just a guess and perhaps there isn't just in case sometimes you would not want that.

 

I'll look more into the gas heating and whatnot. So this upcoming winter, you think I'd benefit financially from having gas heat when it is quite cold outside? There is a setting to use W2/AUX whenever it drops below a set temperature set by you. I think the default is 30F.

[Guest 6.8 AR]

If you're talking about gas as opposed to electric aux heat, I'd think gas wins.

[Fourtyfive]

Dang it , now you have me on the hunt for a new gadget. There goes some gun money .......

[Guest Riciticky]

Make sure electic heat is not running during air conditioning. HVAC/R tech for quite a few moons.