Recent Topics
Let's Talk Porsche 911
by john_pifer - 02/21/20 02:51 AM
CLEARANCE ALERT O'Reilly's Mobil Super Oil
by GMguy84 - 02/21/20 01:27 AM
No more poulan / weedeater at walmart.
by jakewells - 02/21/20 12:44 AM
1991 Land Cruiser FJ80
by CCI - 02/20/20 09:57 PM
Gas price spread
by Chris142 - 02/20/20 09:28 PM
Need an Ecoboost Oil
by kstanf150 - 02/20/20 08:47 PM
2007 sedona
by macdole99 - 02/20/20 08:29 PM
USB-C, USB 3.0, 3.1Gen1, 3.1Gen2 Confusion.
by SubLGT - 02/20/20 08:12 PM
Apple Air Pro 2 tablet, How to send a link by email
by JLawrence08648 - 02/20/20 07:56 PM
Needed A Truck
by MParr - 02/20/20 07:21 PM
Battery Charger/Desulfator
by DBMaster - 02/20/20 06:45 PM
STP 0W-16 found in NC Autozone
by mv6845 - 02/20/20 06:20 PM
Cats
by Anduril - 02/20/20 06:12 PM
Are Onan oil filters now Fleetguard?
by atikovi - 02/20/20 05:57 PM
Car overheating under different conditions.
by MichaelRS - 02/20/20 04:39 PM
2008 CR-V AT Question
by Gebo - 02/20/20 04:18 PM
2019 Sienna
by s2krunner - 02/20/20 04:01 PM
Newest Members
Grennx, coverage, Bubbabighatt, AAIRCraig, Jason454
70763 Registered Users
Who's Online Now
51 registered members (2002 Maxima SE, antone, Amkeer, bbhero, bachman, Aichiguy, 6 invisible), 1,242 guests, and 18 spiders.
Key: Admin, Global Mod, Mod
Forum Statistics
Forums67
Topics301,732
Posts5,201,608
Members70,763
Most Online4,538
Jan 20th, 2020
Donate to BITOG
Print Thread
Hop To
Help me add a C-wire #5310742 01/02/20 07:20 AM
Joined: Dec 2012
Posts: 2,067
R
redhat Offline OP
OP Offline
R
Joined: Dec 2012
Posts: 2,067
[Linked Image from i.imgur.com]

I have an older Janitrol forced-air furnace in my house. I have an old Honeywell programmable battery powered thermostat that has two wires going to it. Red and white. I want to hook up my Nest thermostat and know that it's best to have a common wire. I have tried it without the common and my Nest just short-cycles my furnace. I ran a new 7 wire (to future proof and potential add of A/C) from the thermostat to the furnace.

Anyone have any idea where to add the common wire? In addition to this wiring, I have (but do not use) an air humidifier that is tapped into a water line. I have to look again, but in this Pic, you see the red wire tied to a black wire. I think this goes to the air humidifier so I can probably remove that. The other wire here besides the white is probably the red.

Thanks.


19 F150 2.7 - M1EP 5W-30, FL2062, 11k
17 Taurus Limited AWD - M1EP 5W-20, FL500S, 30k
84 JD 316 Repowered w/Vanguard 18
Re: Help me add a C-wire [Re: redhat] #5310772 01/02/20 07:58 AM
Joined: Mar 2004
Posts: 23,835
D
Donald Offline
Offline
D
Joined: Mar 2004
Posts: 23,835
You need to find the transformer that supplies the 24V. One lead goes to your current thermostat. The other goes to the furnace controls. You want that lead as the common.


2015 Ford F-250 w/Powerstroke
2016 Subaru Crosstrek CVT (wife's)
Re: Help me add a C-wire [Re: redhat] #5310859 01/02/20 09:15 AM
Joined: Aug 2003
Posts: 14,470
R
Rand Offline
Offline
R
Joined: Aug 2003
Posts: 14,470
What Donald said.

https://thesmartcave.com/thermostat-c-wire-common/
Quote
So, the c wire doesn’t actually provide the power. It provides a return path so that the thermostat can be powered without disrupting the other wires which are used as electrical on/off switches for your equipment.


2019 Jeep Cherokee Trailhawk 2.0T
2020 Hyundai Elantra "Value Edition"
Re: Help me add a C-wire [Re: redhat] #5310866 01/02/20 09:30 AM
Joined: Sep 2015
Posts: 2,425
M
mk378 Offline
Offline
M
Joined: Sep 2015
Posts: 2,425
Does the cable with the yellow tag go to the gas valve or to the humidifier?

On a sticker inside the furnace there should be a schematic of the stock wiring, get a picture of that.

Last edited by mk378; 01/02/20 09:34 AM.
Re: Help me add a C-wire [Re: redhat] #5310901 01/02/20 10:07 AM
Joined: May 2013
Posts: 349
F
Fitter30 Offline
Offline
F
Joined: May 2013
Posts: 349
If the furnace board doesn't have the C terminal just use the cabinet and with a meter R to the cabinet should be 24 vac.

Re: Help me add a C-wire [Re: redhat] #5311117 01/02/20 01:57 PM
Joined: Apr 2004
Posts: 5,664
J
JustinH Offline
Offline
J
Joined: Apr 2004
Posts: 5,664
The honeywell smart thermostat I purchased included an adapter to provide power when no C wire is present.

I did not use mine, however my brother has an older furnace with no C wire, and he used his just fine.

The adapter deal is installed inside the furnace, and it was fairly simple to install, he is non technical.

Shut the power off and read the directions I suppose. I would get a C wire adapter on ebay or amazon.


'16 Ford Escape
'11 Scion XB
Re: Help me add a C-wire [Re: redhat] #5311172 01/02/20 02:49 PM
Joined: Oct 2011
Posts: 3,134
B
Brybo86 Offline
Offline
B
Joined: Oct 2011
Posts: 3,134
If you ran a new cable from furnace to thermostat you don't need an adapter, just use a multimeter on furnace control panel to find a constant 24v with furnace at idle, tie in and send that to your nest


12 Honda Odyssey 112k
09 Kymco Super8
08 Honda Accord 2.4L 164k
01 Kymco People 50
95 Yamaha Jog
Re: Help me add a C-wire [Re: redhat] #5311249 01/02/20 04:10 PM
Joined: Sep 2007
Posts: 240
KeithS_NW_Ohio Offline
Offline
Joined: Sep 2007
Posts: 240
The black wire on that transformer is the C wire


2012 Ford Fusion - Mobil 1 0W-20EP/HM
2005 Nissan Altima - Mobil 1 0W-30AFE
Mine to Maintain
2018 Jeep� Compass - Mobil 1 0W-20EP
Re: Help me add a C-wire [Re: redhat] #5311299 01/02/20 04:49 PM
Joined: May 2013
Posts: 386
M
M56959 Offline
Global Moderator
Offline
Global Moderator
M
Joined: May 2013
Posts: 386
Please refrain from posting if you cannot be helpful and civil. I've removed the posts that weren't helpful.

Re: Help me add a C-wire [Re: redhat] #5311862 01/03/20 07:11 AM
Joined: Dec 2012
Posts: 2,067
R
redhat Offline OP
OP Offline
R
Joined: Dec 2012
Posts: 2,067
Thank you all for the info. I will be looking at this hopefully tomorrow morning and I'll post back. I have a multimeter and will check too if need be. Thanks.


19 F150 2.7 - M1EP 5W-30, FL2062, 11k
17 Taurus Limited AWD - M1EP 5W-20, FL500S, 30k
84 JD 316 Repowered w/Vanguard 18
Re: Help me add a C-wire [Re: redhat] #5333842 01/27/20 02:51 PM
Joined: Mar 2010
Posts: 656
M
mx5miata Offline
Offline
M
Joined: Mar 2010
Posts: 656
Do you have a G - fan terminal?


NAPA FULL SYNTHETIC 0w20 Partsplus oil filter
Wix air filter
Previous Thread
Index
Next Thread

BOB IS THE OIL GUY® Powered by UBB.threads™