Questions tagged [thermostat-c-wire]

The "C" or Common wire provides a way to get constant 24VAC power to the thermostat, now required by many newer thermostats with WiFi and/or touchscreens.

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3answers
770 views

Wiring for ecobee3 lite

I recently purchased the ecobee3 lite and am now stuck trying to install them. I have 3 Honeywell thermostats I am looking to replace and my heating system is oil/hot water. My home was built in 1970 ...
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2answers
2k views

Isolation relay for Ecobee smart thermostat: NC or NO?

I've been looking for "isolation relays" to install an Ecobee 3 smart thermostat on my 2-wire T/T furnace (replacing a Honeywell round thermostat). I know I want to use the 24VAC transformer/relay ...
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1answer
4k views

Where to connect c wire at furnace for Honeywell Wi-FI thermostat

We are installing a new honeywell wifi thermostat have an extra blue wire in our bundle. We aren't sure where to connect the blue wire on the furnace board. Click for larger view
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102 views

Need to identify a common wire on my old HVAC

For Nest Thermostat 3, I am trying to identify a common wire on my old HVAC. The diagram can be found on the link below:
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2answers
5k views

Where do I connect a C wire in an old Furnace?

I am hoping to be able to upgrade to a smart thermostat but unfortunately my furnace doesn't have the "easy" option with an obvious C terminal. My furnace is OLD but it actually has the full 5 ...
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2answers
72 views

Gas Furnace only, is Y wire needed?

I have force air (propane furnace). I would like to upgrade to a new "smart" thermostat, but they didn't run a C (common) wire which is required for most of these units to run properly. I do however,...
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2answers
861 views

How to add C-wire from Laars mini-term

Folks, I am having problems connecting my Nest thermostat to a boiler. Given Laars Mini-term JVS series with Temperature Control PCB Module (pictured below) When I short Com call and Heat call wires ...
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1answer
165 views

How to identify the C terminal on my HVAC [duplicate]

As you can see I have a Y G W R/2 C/3 D/1 terminals on my HVAC. I am planning to change my thermostat to one that requires a c line. There are 2 spare lines available, however I am not sure which is ...
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1answer
2k views

Honeywell Zone System Wiring

I have a Goodman HVAC system that is split into three zones. I wanted to upgrade to programmable thermostats, so I picked up three Honeywell RTH8580WF. Reading through the descriptions I noted they ...
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2answers
180 views

Where do I connect a C-wire on my Honeywell TrueZone board?

My Honeywell TrueZone 311 board does not have a terminal for the blue wire. Where does it go? I plugged in the wires for the dampers and the thermostats, but the five wires from the furnace to the ...
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2answers
88 views

Just another C wire problem

Sorry for the long post but if you can make it to the end, I would greatly appreciate it. I have what I believe to be an uncommon situation that I haven't been able to solve. I have a thermostat that ...
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2answers
3k views

Is the transformer bad on my Central Air Conditioner?

Need some help diagnosing a problem. My very old central AC unit isn't working. It's just AC and about a year ago I connected a C-Wire to the air handler when swapping the thermostat for a wifi ...
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1answer
80 views

Nest thermostat to Kelvinator furnace

My old thermostat had 4 wires. I replaced with a Nest thermostat. At times the AC condenser is running but the furnace blower is not running. Found other with this and they said need to add common ...
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1answer
39 views

Wifi thermostat

Can I connect C-wire to the empty terminal(red arrow)
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1answer
1k views

Where to connect c wire in furnace?

I'm trying to figure out where to connect a C wire from a thermostat to my furnace. I found this old post for the same furnace type (Trane XE70), but it seems as though a red wire goes to the terminal ...
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0answers
1k views

Why does my Nest thermostat report error e195 when I try to use the air conditioning?

I had a Nest E installed in February and it has worked really well until it was time to turn on the AC. Now I get random e195 errors (no power detected to the R wire). The most likely answer from my ...
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1answer
377 views

Adding Unused C-Wire for Nest Thermostat

I'm having an issue with my NEST thermostat short cycling my air handler fan while in running AC. This is a known issue, and the fix seems to be adding a common wire to the NEST. My thermostat is ...
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1answer
1k views

Where should I connect a C wire on my Goodman PGB030075-1 furnace?

Is this where I can piggyback for c wire on Vine thermostat? Thanks
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1answer
277 views

Adding C wire to WiFi thermostat

I’m trying to add c wire to furnace to run a WiFi thermostat but don’t know where to hook up c wire to get power to turn on thermostat i have 2 extra wires just don’t know where to put one them to get ...
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1answer
41 views

C wire problem for WiFi thermostat [duplicate]

I’m trying to add c wire to furnace to run a WiFi thermostat but don’t know where to hook up c wire to get power to turn on thermostati have 2 extra wires just don’t know where to put one them to get ...
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5answers
77k views

Why is my Nest thermostat not working with A/C?

I installed Nest thermostat a few weeks ago, replacing an old Lux programmable thermostat (there was nothing wrong with it). I connected 4 wires (R,W,Y and G) to the Nest. But as soon as I'd ...
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1answer
1k views

Where do attach C wire on my boiler?

I need to add a C wire to use my wifi thermostat. I have a 2 wire thermostat now. There is a third wire in the wall which runs to the basement where it is cut off. I can easily extend it to the boiler....
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1answer
3k views

Can a Ground Wire be attatched to a nail in wood stud?

Guilty as assumed: I've installed a thermostat connected to a single electric baseboard. Is it possible to connect the load and line ground wires to a nail which is attached to a wood stud? OR, simply ...
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1answer
372 views

What are these extra wires behind my thermostat?

I an hoping to install a new thermostat that requires a C wire. I pulled off my old thermostat, an old round dial type, and it was of course only connected to four wires. The four wires are the only ...
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1answer
2k views

Nest, Blue Wire, W1 and W2

I just got a Nest E thermostat and I'm trying to hook it up. There is a blue wire that I had assumed was the "C" wire, but looking at the furnace, it doesn't look like that's the case, as the blue ...
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0answers
191 views

Connect C wire to Carrier board

I got Carrier board HK61EA010 and extra C-blue wire that is not connected to the board. I wanna use this wire to power WI-FI thermostat. I cannot find the manual for this board. Does anyone know where ...
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1answer
690 views

how to connect C wire to Weil-McLain EG-65 Series-5 gas steam boiler

Which of the Weil-McLain EG-65 transformer terminal should I use for a thermostat common wire? (I am trying to connect a nest learning thermostat to that boiler and it needs a common wire). Thanks.
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1answer
947 views

Wiring a new thermostat without a C wire, extra wires from furnace

I have checked other posts regarding this and don't see a solution yet. I have purchased a new thermostat that requires a c wire. My old thermostat's c wire didn't work so I went ahead and added a ...
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1answer
466 views

Installing a smart thermometer (ecobee4) can I move the wires around on the HVAC?

I want to install an ecobee4. I want to install it with the C wire so I do not need to use their kit. It seems to me that I should be able to just move the wires around on my hvac. Here is a diagram ...
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2answers
11k views

Less than 24 volts on the thermostat C wire

We have a brand new air handler at work, but the thermostat is mounted on a wall next to a server/computer room which is always warmer than the rest of the office. I want to install a thermostat that ...
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1answer
503 views

Install Common Wire (unable to find terminal or 24 VAC)

I bought a Nest 3rd Generation Thermostat. Live in a 2 family home, where my floor/basement has the boiler room/furnace. I have a Laars Mini Therm Furnace Model JVT. There's a thermostat upstairs as ...
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1answer
542 views

How do I wire a thermostat with an external 24V transformer?

My current wiring has 5 wires, R, Rc, Y, G, and W wires. No C wire. I've added an external 24V transformer and connected one wire to the C connector but don't know what to do with the other. If I ...
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2answers
33 views

Home thermostat woes

I tried to switch to a new smart thermostat in my home. When I was adding it, something happened. The new thermostat didn't show any power (And yes, the C wire was plugged in). Not knowing what else ...
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3answers
5k views

How to move from RH/RC thermostat to C thermostat in AC only system?

I see this is a pretty common question, but the answer seems like it might be dependent on your thermostat and air handler, so I'm posting with my specific questions. I'm upgrading from a White ...
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3answers
2k views

Wifi Thermostat wiring

Replacing 2 Hunter thermostats with a Honeywell RTH9580 Wifi. Neither unit has a C wire - I'm comfortable with the upstairs high efficiency unit, but the downstairs older unit has thrown me for a loop....
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3answers
225 views

Confirming C wire in my thermostat

can someone confirm that the blue wire is the "C wire"? What are the other wires (yellow, light pink, brown, and orange) that are not connected to anything?
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0answers
822 views

Need Help on Adding a Common Wire for Nest

I recently purchased a Nest thermostat. After couple weeks of usage, the Nest is constantly shut down due to low battery. I search online that adding a common wire is the go solution for this. However,...
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1answer
818 views

Wiring C-wire in old Rheem

looking for some help with an old Rheem 1005 HVAC system. I’ve scoured the Internet for days, so this is a last ditch effort at self-help. I’m installing an ecobee to an existing 4-wire system that ...
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0answers
759 views

Honeywell WiFi thermostat jumper loop separate ac and gas furnace

I need to validate my understanding for the installation of a WiFi thermostat that requires 24volt continuous power to operate in a constant state. I am DIYer who is computer literate. Like a number ...
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2answers
450 views

can I use an unused y2 or w2 aux wire and connect to the C terminal

I got a new ecobee thermostat that requires a c wire. my current thermostat has 4 wires plugged in, and there are 2 extra wires not being used coming out of the wall one blue labled y2, and a brown ...
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0answers
2k views

Old oil furnace with 2 wire thermostat, installing new wifi and need C wire. How can I wire with my current stack switch?

I'm trying to wire a new wifi thermostat and only have two wires, R and W. The stack switch (transformer - pictured) only has two wire slots as well. What is the easiest way to add a common C wire? ...
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2answers
1k views

Can I use the Y wire in place of the C wire for my new thermostat?

I'm looking to wire a Honeywell Lyric T5 to my furnace (I do not have an air conditioner, I do have a humidistat). My current wiring at the thermostat is G,W,Y,R. At the furnace it's G,R,C, and 2 at W,...
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3answers
3k views

Where should I connect the C wire in a Janitrol furnace?

I currently have a Honeywell Thermostat with 4 wires going to a Janitrol Furnace. I am trying to install a Honeywell WiFi Thermostat RTH6580WF and I'm missing my C wire. My bundle has 8 possible ...
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1answer
244 views

Wiring new 'c' wire to heat pump system. Do I need to connect at both air handler and condenser?

I am planning on installing a new WIFI thermostat (Honeywell RTH6580WF). I have a heat pump system (outdoor condenser unit and air handler in attic). Old thermostat did not have a 'c' wire, but it ...
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0answers
91 views

Why doesn't my thermostat work?

I replaced old thermostat with Honeywell wifi and added C wire from furnace to new thermostat. I left the jumper wire on Rc and R in place and wifi would not come on line. Checked C wire and have ...
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1answer
130 views

Can I use the extra thermostat cable as C cable for wifi?

I just purchased an ecobee4 and I found that I need C wire for wifi which is not connected to my current thermostat. However, there 2 extra wires I found in the wall. Could you use one of them for the ...
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1answer
13k views

Nest thermostat not turning on heat

I have an old gas furnace/boiler for hot water baseboard heat and I'm trying to switch from a 2 wire mercury bulb thermostat to a Nest Thermostat "E" (the new white faced one). There are 5 wires in ...
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1answer
206 views

Where to connect c wire

I’m installing a new WiFi thermostat that needs the c wire. I ended up running new thermostat wires that contained the common wire but now I’m stuck on where to connect it to the furnace. Can ...
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1answer
486 views

C Wire for Thermostat

I am upgrading my thermostat (Have AC & Heat) and found that it doesn't have the "C" wire that I need to power my new thermostat. The furnace does have a terminal for C, but only condensation pump ...
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3answers
13k views

How can I wire my WIFI thermostat to control my millivolt fireplace?

I have a gas fireplace that has an millivolt on/off switch on my wall (and a remote that includes flame on/off, a countdown timer and a thermostatic flame control). I want to be able to program ...