Linked Questions

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
118k 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
143k 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
99k 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
53k 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
32k 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
  • 3,948
1 vote
3 answers
42k 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
1 vote
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
  • 13
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

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