Nest Learning Thermostat 3rd Generation

nyteacher78

Hello! I hope someone can provide me with some guidance. I have a heating and a cooling system hooked up to my nest 3rd gen learning thermostat. 

I have Y1, G and Rc and then W1 and Rh. Thermostat worked fine for about three years.

Now Nest support tells me I need a C wire. 

My question is, if I simply move the G wire to the C connection on the thermostat, can that G wire act as the C wire?

best

nyteacher78

To add to this I have a Red, White and green coming from our AC panel in the attic and Red and White from the furnace. 

ratio

No. You will most likely need to run a new multi conductor cable from one unit or the other.

nyteacher78

At the air handler the green connects to a green the red to a red and the white to the white that goes outside. 

ratio

The red in the air handler is the 24 volt power, the green is the fan call, the white coming from the stat is the cooling call, & the white coming out of the air handler (& connected to the wire going out to the outdoor unit) is the common that you need to extend to the Nest.

HVACNUT

Assuming Rh and W go to a completely seperate appliance (you say furnace. I'm guessing boiler), then you can substitute the Green wire and connect it to Common on the thermostat and air handler. 
Common on the air handler is the Blue dot.
Splice Green from the air handler to the whites (Grey dot, which should be Y at the thermostat) to energize the fan relay on a cooling call. 
The drawback of course is you won't be able to run the fan only. 

nyteacher78

HVACNUT said:

Assuming Rh and W go to a completely seperate appliance (you say furnace. I'm guessing boiler), then you can substitute the Green wire and connect it to Common on the thermostat and air handler. 
Common on the air handler is the Blue dot.
Splice Green from the air handler to the whites (Grey dot, which should be Y at the thermostat) to energize the fan relay on a cooling call. 
The drawback of course is you won't be able to run the fan only. 

Thank you…yea Rh and W go to the boiler down stairs. 

I’m not following you though. Do I run a new wire from the the air handler blue dot to the whites grey dot. Then connect the green from the thermostat to the grey dot?

HVACNUT

nyteacher78 said:

HVACNUT said:

Assuming Rh and W go to a completely seperate appliance (you say furnace. I'm guessing boiler), then you can substitute the Green wire and connect it to Common on the thermostat and air handler. 
Common on the air handler is the Blue dot.
Splice Green from the air handler to the whites (Grey dot, which should be Y at the thermostat) to energize the fan relay on a cooling call. 
The drawback of course is you won't be able to run the fan only. 

Thank you…yea Rh and W go to the boiler down stairs. 

I’m not following you though. Do I run a new wire from the the air handler blue dot to the whites grey dot. Then connect the green from the thermostat to the grey dot?

Connect Green wire to C on the thermostat and Blue dot splice. 
Connect Green from air handler to grey dot splice. 

ratio

I think that picture is the air handler & the 3 conductor with the green wrapped around is the wire going out to the condenser. @nyteacher78, is that not the case?

If so, it's not going to where we need it.

pecmsg

Do a search of Issues with the NEST............Then get a different t-stat.

nyteacher78

ratio said:

I think that picture is the air handler & the 3 conductor with the green wrapped around is the wire going out to the condenser. @nyteacher78, is that not the case?

If so, it's not going to where we need it.

Hi sorry I was away for thanksgiving I’m heading up into attic to take a look I’ll post a new picture

nyteacher78

HVACNUT said:

nyteacher78 said:

HVACNUT said:

Assuming Rh and W go to a completely seperate appliance (you say furnace. I'm guessing boiler), then you can substitute the Green wire and connect it to Common on the thermostat and air handler. 
Common on the air handler is the Blue dot.
Splice Green from the air handler to the whites (Grey dot, which should be Y at the thermostat) to energize the fan relay on a cooling call. 
The drawback of course is you won't be able to run the fan only. 

Thank you…yea Rh and W go to the boiler down stairs. 

I’m not following you though. Do I run a new wire from the the air handler blue dot to the whites grey dot. Then connect the green from the thermostat to the grey dot?

Connect Green wire to C on the thermostat and Blue dot splice. 
Connect Green from air handler to grey dot splice. 

The the connection with the green wire wrapped around it goes outside to the condenser 

The red from the condenser  connection goes to this

The blue goes to that as well 

pecmsg

NEST
****
! ! !

nyteacher78

pecmsg said:

NEST
****
! ! !

Harsh. I have three others and this is the only one I’ve ever had an issue with. Their support is terrible even though this one is just two years old it’s out of warranty and they will not replace the battery. I actually bought an after market battery and replaced it but that do not help. Last ditch effort so I don’t have to drop money is to use a c wire to power it…

pecmsg

NEST is our biggest issue when it comes to modern equipment. 

Your happy fine!

nyteacher78

HVACNUT said:

Assuming Rh and W go to a completely seperate appliance (you say furnace. I'm guessing boiler), then you can substitute the Green wire and connect it to Common on the thermostat and air handler. 
Common on the air handler is the Blue dot.
Splice Green from the air handler to the whites (Grey dot, which should be Y at the thermostat) to energize the fan relay on a cooling call. 
The drawback of course is you won't be able to run the fan only. 

So I followed this exactly. From the T-stat the red goes to red at air handler, white goes to the white from the condenser and the green from the air handler. 

T-stat green goes to connection with the red from condenser and the white from the drip pan pump which goes to that little pump then to the blue at the air handler…..

nest recognizes the c wire….tested ac and the fan does kick on as expected and condenser…heat works as well…

did I do this right? Don’t want to damage anything…thank you!

pecmsg

Just get a different stat!

Jamie Hall

nyteacher78 said:

HVACNUT said:

Assuming Rh and W go to a completely seperate appliance (you say furnace. I'm guessing boiler), then you can substitute the Green wire and connect it to Common on the thermostat and air handler. 
Common on the air handler is the Blue dot.
Splice Green from the air handler to the whites (Grey dot, which should be Y at the thermostat) to energize the fan relay on a cooling call. 
The drawback of course is you won't be able to run the fan only. 

So I followed this exactly. From the T-stat the red goes to red at air handler, white goes to the white from the condenser and the green from the air handler. 

T-stat green goes to connection with the red from condenser and the white from the drip pan pump which goes to that little pump then to the blue at the air handler…..

nest recognizes the c wire….tested ac and the fan does kick on as expected and condenser…heat works as well…

did I do this right? Don’t want to damage anything…thank you!

If it works and doesn't let smoke out of something, leave it alone. Nest wiring in more complex systems borders on a black art...