Linked Questions

0 votes
2 answers
8k views

Where do I connect a C wire in a Rheem Furnace REAB 1415J? [duplicate]

I'm upgrading the thermostat with a Honeywell wifi one. I found all cables at the thermostat end, but can't figure out where to connect the C wire to the furnace (Rheem REAB 1415J).
GeneB's user avatar
  • 1
0 votes
1 answer
2k views

Is it possible to use add-a-wire with my current configuration to add a C-Wire? [duplicate]

I only have four wires: Red, Blue, Yellow, and Green. My old thermostat jumps the R to RC and leaves C empty. I have a new thermostat that wants 5 wires, but I don't have C. I am not sure what the ...
Machinus's user avatar
0 votes
1 answer
988 views

Where is my Common Wire? [duplicate]

I purchased a wifi thermostat and cannot located the common wire. My unit is old and is a Coleman 70 with no terminals inside labeling the wires. As you can see in the second image, there is a blue ...
Brian Orta's user avatar
0 votes
1 answer
2k views

Options for adding “C” wire to thermostat [duplicate]

Possible Duplicate: Options for adding “C” wire to thermostat I am upgrading to a newer thermostat that requires a constant 24 volt feed, I have an extra (unsused) wire in the cable ...
John Waters's user avatar
0 votes
1 answer
851 views

How can I get my thermostat C wire connected? [duplicate]

I have an older furnace, on the switch block I have Y,C.W,R and an unlabeled screw that connects to the shut off it looks like. I need to hook up a thermostat that needs the C wire. I have a spare ...
Brian Miller's user avatar
0 votes
1 answer
1k views

Need to know where to connect my C wire [duplicate]

I had the extra wire in the wires run from my thermostat to my A/C, but the old thermostat did not need the C wire, so it was cut and stuff on both ends. While installing the new thermostat I ...
Nate's user avatar
  • 1
1 vote
1 answer
948 views

thermostat c wire question [duplicate]

I am looking to install a new thermostat that will require a C wire. I have a single stage A/C unit and my current thermostat has Rc, G, and Y wires. There is also an unused blue wire which I traced ...
Patrick's user avatar
  • 11
0 votes
1 answer
820 views

How can I implement an unused wire as a C wire for my thermostat? [duplicate]

I have a boiler system that uses 2 wires to the thermostat. I am going to buy a new thermostat that needs a C wire. There is a spare wire not being used and it is not hooked up to anything. How can I ...
Elliott's user avatar
0 votes
1 answer
636 views

HVAV no C terminal but available wires [duplicate]

Pretty common problem here but the posts I've seen are a little different. New Wi-Fi tstat, no C terminal at furnace but plenty of available wiring at both ends. Unlike others problems posted of ...
NikM's user avatar
  • 1
1 vote
2 answers
520 views

Where to connect the C Wire? See pictures and diagram [duplicate]

I have Rheem RBHC-14A00NFA AC unit. I am trying to install nest thermostat but don’t know where to connect the C wire. I am attaching the picture of the wires and the diagram. Please help! Thanks
scottmeyer's user avatar
1 vote
1 answer
383 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 ...
Abner Sassoon's user avatar
1 vote
1 answer
361 views

Adding a "C" wire for a wireless theromstat [duplicate]

I have a heat only system with two wires leading to the thermostat - red and white - and am wanting to add a wireless thermostat. The new thermostat however requires a "C" wire. Can I add a C wire?
RJJ's user avatar
  • 11
0 votes
1 answer
275 views

How do I create a C wire? [duplicate]

My furnace is old and only has 4 wire connections, but I require a C wire. How can I create one based on this diagram? I do have 5 wires running between the furnace and thermostat.
Michelle Bergeron's user avatar
1 vote
0 answers
348 views

How can I add a common "C" wire to my thermostat? [duplicate]

Possible Duplicate: Options for adding “C” wire to thermostat I recently bought the Honeywell THM5320R Wireless thermostat. After going to hook it up I found what many others have, it requires a ...
J. Edwards's user avatar
0 votes
1 answer
221 views

What powers a Nest thermostat? [duplicate]

I have an older thermostat I'd like to replace with the more modern Nest thermostat. The online Nest compatibility checker tells me that I have a compatible device. However, I'm not sure how it could ...
Chris's user avatar
  • 47
1 vote
0 answers
25 views

How to add extra 24VAC wire (C wire) [duplicate]

I have recently bought a Honeywell rth9580 programmable WiFi thermostat. Unfortunately I have old electric heating/cooling system probably from 70's. The system is based on two relays (I guess ...
Konrad Nowak's user avatar
12 votes
2 answers
119k views

How do I identify the C terminal on my HVAC?

How do I identify the C terminal on an HVAC, furnace, or boiler? If the terminals don't have a screw labeled C what should I look for on the wiring diagram? What steps should I take if a wiring ...
BMitch's user avatar
  • 42.9k
3 votes
4 answers
20k views

If neutral carries current back to the breaker panel, why doesn't it need to be connected to a switch?

I've got some limited field experience as an electrical helper, but no real classroom experience yet. (saving up for school) I am of the understanding that the neutral wire carries electricity back ...
crush's user avatar
  • 215
4 votes
2 answers
350k views

How can I test whether my furnace issue is the limit switch or the thermostat?

I suspected this issue during the winter and confirmed it now in the summer. Regardless of the temp in my home, the blower motor runs non-stop. In the winter this must have been causing my home to got ...
kareem's user avatar
  • 165
7 votes
1 answer
144k views

On a thermostat, are "R" and "Rh" terminals the same thing?

I have an older thermostat controlling an old ass Trane furnace with A/C. It has an "R" terminal and an "Rc" terminal (they are jumpered - see photo). I see references to an "Rh" terminal online. Are ...
AwesomePossum's user avatar
4 votes
8 answers
100k views

How can I use a separate transformer to provide a C wire to my thermostat?

Update 02/02/2019 I appreciate all the responses and help but unfortunately i must have not seen the emails stating there were responses! I am now looking into a NEST thermostat and was curious if ...
user11748's user avatar
5 votes
5 answers
54k views

Adding a C wire to a new Honeywell WIfi Thermostat

I am trying to install a new Honeywell touchscreen WIFI thermostat and need to add a C wire to my terminal inside the furnace (using the help found at How can I add a "C" wire to my ...
user20715's user avatar
1 vote
8 answers
24k views

I am installing a Honeywell RTH6580WF with a TACO SR504

The current installation does not have a C wire. So I have run an extra wire and am now confused as to where to connect it. There is a 24VAC connection and a common connection. Comments say that ...
Ralph Pass's user avatar
3 votes
5 answers
33k views

HoneyWell Wifi Thermostat and C wire

I just bought the HoneyWell Wifi thermostat and so wanna use it. However my old Thermostat was battery powered and does not use the "C" wire. I opened up my panel and found that there were three ...
Ank's user avatar
  • 131
2 votes
2 answers
11k views

How do I connect a WiFi thermostat to my furnace's primary control?

I would like to install a Honeywell WiFi controlled thermostat to connect to a Honeywell R7184U primary control. My question concerns the "C" wire. The R7184 has the terminals labeled 1, 2, 3 and 4 ...
brian m brouillette's user avatar
4 votes
6 answers
6k views

Connection for C wire on Mastertrol Mark V zone control panel

I have spent hours searching the web for information on this 20+ year old zone control panel, which supports 3 zones of Heat and A/C. The thermostat I'm replacing (on Zone 3) connects to T4/T5/T6 as ...
TomG's user avatar
  • 3,958
1 vote
3 answers
43k views

How do I connect the common wire in a Carrier air handler?

I am trying to install a new wifi thermostat in my home and need to locate the common terminal for my air handler. I have a Carrier model FB4CNF030. It's a new construction home and I have the blue ...
techguy817's user avatar
2 votes
5 answers
5k views

Can I provide a secondary power source for my thermostat?

The thermostat at my home is set up with only the 24 power and return through the relay. I would like to add a 'smart' thermostat, however the line is fairly well buried in the wall/basement ceiling ...
Mike's user avatar
  • 23
0 votes
1 answer
18k views

Wireless Thermostat C-Wire Substitute

I've read How can I add a "C" wire to my thermostat? and checked out the Venstar Add-A-Wire Accessory. I've watched Honeywell's YouTube video on "DIY Wi-Fi Thermostat Substitute G-Wire for C-Wire," ...
Kermit's user avatar
  • 1,228
2 votes
2 answers
14k views

Adding a C Wire using a 24V AC Transformer to a 2 Wire Heating System for Nest

Continuation from Can I use any of my existing oil control terminals (TTFFAA) for a C wire? EDIT: Wanted to finally say this is SOLVED with help from @JPhi1618 (see conversation below). If you have a ...
Teuszie's user avatar
  • 33
3 votes
3 answers
12k views

Where's the C terminal on my boiler control?

The new thermostat I purchased doesn't run on batteries, and needs 24 volt power. I have only a red and a white wire connected between the boiler and the thermostat, but there is also a third, unused ...
Mike N's user avatar
  • 31
0 votes
1 answer
23k views

How to connect thermostat C wire to Weil-McLain CGa boiler? [duplicate]

I have Weil-McLain gas boiler for hot water heat and going to install WiFi thermostat that requires common 24V 'C' wire. I do have a free wire in the cable but cannot figure out where should I connect ...
Dmitriy's user avatar
2 votes
1 answer
17k views

How do we replace an old 3-wire thermostat with a 4-wire one?

How do we replace an old 3 wire thermostat with a 4 wire one? We have an AC/heating unit, but the wiring for the thermostat does not have a yellow wire. What can we do?
Irene's user avatar
  • 21
2 votes
2 answers
10k views

Can I use a WiFi thermostat without a C wire?

I have a very old Honeywell programmable thermostat. I am going to replace it with a White-Rodgers UP500W Emerson Sensi WiFi Thermostat. I just want to know if the WiFi unit will work without a C ...
qinking126's user avatar
0 votes
3 answers
13k 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 ...
Fuzz Evans's user avatar
0 votes
1 answer
11k views

Why isn't the "C" or Common wire working on my Nest thermostat?

I Have connected the Blue wire to the C terminal on a 3rd Generation Nest and to the Blue wires on the Transformer....... But the Nest Thermostat does not show the Blue wire connected on the Equipment ...
Ed J Panco's user avatar
2 votes
2 answers
6k views

How do RH/RC/R and Y/W relate for HVAC?

I have the following notes for HVAC (that I've compiled from reading through here): Thermostat wiring: C low voltage power wire that brings power from heating/cooling equipment to thermostat ...
user avatar
3 votes
1 answer
7k views

How can I add a "C" common wire to this system? [duplicate]

I would like to add a "C" / Common wire hookup to my hvac system and get a fancy new thermostat. I've read How can I add a "C" wire to my thermostat? and still have some questions. First of ...
Raolin's user avatar
  • 133
3 votes
2 answers
3k views

Can I use an unused wire as a "C" wire?

I just bought a new thermostat that is Wi-Fi enabled and it requires connection to a "C" wire. The old thermostat does not have one running to it, but there are other unused wires. The thermostat ...
user14503's user avatar
1 vote
0 answers
5k views

How can I add a common wire to the existing furnace wiring?

My current furnace has Rh and W1 to the thermostat. I'd like to add a C for my new networked thermostat, but I'm not sure where to connect it. From my research it sounds like I should be able to just ...
fracai's user avatar
  • 111
3 votes
2 answers
2k views

Can I use the unused blue wire as a C wire?

I'm installing a wifi-capable thermostat in my house which for obvious reasons requires a C wire. The old school mercury thermostat I'm replacing didnt have a C wire connected but I've checked the ...
J. Smith's user avatar
1 vote
2 answers
3k 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,...
RookieMistake's user avatar
0 votes
1 answer
3k views

Can I directly add a Common wire to this point on a 24VAC transformer, or will load be too high? (70mA)

Referencing This excellent answer I have a two wire furnace controller, 24VAC, no common. I measured the current draw of the relay (when the thermostat wires are shorted), it draws 0.2A Wish to add an ...
Mtl Dev's user avatar
  • 133
0 votes
1 answer
3k views

Add a c-wire to 25+ year old Rheem furnace

I've looked at just about every post on adding a C-wire to power a WiFi thermostat but remain uncertain on how to proceed. The current installation on a Rheem RGAC-080A is two wire as here: XFMR - ...
geoB's user avatar
  • 211
1 vote
1 answer
3k views

How do I connect a C-wire on a Triangle Tube Prestige Solo 110? [duplicate]

I purchased a Honeywell RTH6580WF to use with my recently installed Triangle Tube Prestige Solo 110 propane boiler. I only have two wires at my existing heat-only thermostat. I understand that the c-...
Jon's user avatar
  • 11
1 vote
1 answer
2k views

How to troubleshoot heat that's always on?

My boiler (Weil Mclain CGA Gold ~2003 install) failed the other day. After some help from a plumber and reading the manual, I replaced a few parts (more below) to get it running again. Now one zone is ...
Yann's user avatar
  • 111
1 vote
3 answers
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....
Chris's user avatar
  • 11
0 votes
1 answer
2k views

Can I share "C" wire on two thermostats?

I am wiring a second thermostat right next to the original one. The new needs a C wire. Can I share it from the old one? Old: 8 wires, used to run heat pump (w/ heating and AC) and backup oil. Now ...
mankoff's user avatar
  • 514
2 votes
2 answers
1k views

Can I pull a common wire off an evaporative cooler transformer relay?

I have a Nest thermostat currently controlling a LP furnace. The old thermostat didn't have a common wire connected, but there was a an extra wire in the bundle and a common terminal on the furnace ...
Matt's user avatar
  • 183
0 votes
1 answer
2k views

Add C wire to very old gas furnace

There is a very old gas furnace in our attic. It has a two-wire transformer and no obvious terminals to expand. I need to run a C wire to my nest thermostat, which I'm planning to do via their nest ...
justinbelcher's user avatar

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