Linked Questions

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
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
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
5 votes
1 answer
566 views

Adding a C wire to older 3 wire

How do I use the green wire as a C wire as suggested in most installation instructions for the newer wi-fi thermostats? They all reference terminal strips at the furnace, all I have is the 3 wire ...
Paul's user avatar
  • 51
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
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
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
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
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
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
3 votes
1 answer
448 views

Can't find HVAC C terminal

Could any of these be the c terminal on my hvac unit? There's already a c wire there, just can't figure out where to connect it.
Misty 's user avatar
  • 31
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
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
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
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

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