How to Connect an Unused C Wire (Common Wire)

[@karenbaggs7731]

Rob! You are awesome! I am a 58 yo nurse and was able to get the C wire connected for our new Nest Learning Thermostat. I scoured the internet and KZbin and finally found exactly the information needed thanks to you. Thank you so much for your help!

[@randalljabeth4396]

Thank You! I tried to install a new WiFi thermostat and my C-wire wasn't working. I was ready to return it to Home Depot until I saw your video. The C-wire was disconnected at the furnace. I looked at the wiring diagram on the furnace and found where I needed to connect the T-wire. Hooked the new Thermostat up and it worked. Love the video. Thanks again

[@yamileemigliori4]

Wow, you're a life saver! You're the only one that I found that explained how to connect the C-wire when you do not have the letter panel on your inside unit. I was about to go buy the cheap thermostat again and forget the smart thermostat. THANK YOU THANK YOU for making this video.

[@BishopDelicious]

Rob, thank you! I installed a Nest thermostat and it clearly needed a C wire. After tearing open my furnace, I found I didn’t have a “terminal” so to speak… I searched high and low, including the HVAC manual… And nothing resembled what I was seeing. Your video was truly the only thing out there that showed how to tap into a non-terminal system. I followed your lead and tapped C wire into the AC to common and everything is humming perfectly now. I can’t thank you enough.

[@jimmyengstrom1068]

Like so many others have said, THANK YOU for this video!! In my situation I had an older "non-smart" thermostat downstairs that controlled both a steam boiler for heating, as well as a central air unit that I wanted to upgrade as my local utility was basically giving away the Emerson Sensi smart-thermostat. The thermostat wire going up to the Air Handler in the attic did have an "unused" blue Common wire but when I went upstairs in the attic I saw that it was not connected to anything. I saw that the wire that goes out to the compressor outside for the AC had two cables that were pigtailed into others outside the AC Handler. The White wire was connected to a wire that was then connected to the Yellow "Y" cable going to my thermostat so watching your video I was then able to figure out that the other wire (the red one that was connected to a Brown wire that went to the control board inside the AC handler) was the 'common wire' in that circuit so I simply did pretty much what you did in the video, turned off the power and then pigtailed the blue common wire to to the same junction as the red/brown wire and voila! It worked!! the only difference was that in my case I had to do an extra pigtail connection at the thermostat wire to 'extend' the C wire from the thermostat to the junction where the red/brown wire was connected.

[@JorgeGonzalez-yt8sy]

after many videos and forums, this is the vid that helped the most. we have an old a/c from the 80's. whoever installed it used two bundles of wires, one for the thermostat and the other for the condenser (i.e. instead of low voltage two wire, they used another thermostat wire; i guess that's what they had on-hand). then they connected the yellow wire from the thermostat to the red wire of the condenser, i guess to make it more confusing. so following what you said at about the 4:35 mark, i connected the unconnected blue C wire of the thermostat bundle to the opposite of the yellow wire which for me was a white wire connected to a terminal block with a label of "3" (which i haven't seen in any videos or forums). this vid combined with the wiring diagram made me confident that the "3" was the common. thank you very much !

[@BishopDelicious]

Same! I can’t believe it’s so hard to get this info. Perhaps HVAC guys are keeping it on the low. I looked for a long time, this video is what gave me the confidence to get it done.

[@mannycaz9085]

This was exactly situation. An old A/C unit without a control board. This video helped me so much. Luckily there was an unused C-Wire, no Ecobee PEK for me.

[@4ac5cabc56]

Super helpful! This was the only video I could find showing how to attach the wire to a unit without a control board. Just successfully hooked mine up. Thank you!

[@RobSomeKnowledge]

Hahah I was in the exact scenario of not being able to find a video, so thats why I made this one :) Im glad it helped you out and continues to help so many people, even 4 years later!!!

[@davidwferrar]

Great little video. Just as you described. Found blue wire tucked away behind old thermostat and went straight to the same blue wire within my air con unit. Took me all of 2 minutes to identify and connect up. Now all working fine with wifi connected. Thank you. Keep up the good work

[@Marlin365]

Awesome video, I had 5 phone calls with the Honeywell T9 techs, and no joy. My air handler has no control board. Within 20 minutes of watching your video, I was able to get it working, since you showed which wire to connect for the Common!

[@JDSileo]

This was amazingly helpful. I moved to a condo that didnt have the C wire used. The explanations of the wires going to the compressor helped me trace where the C wire ought to go. and Boom! I have a smart thermostat again.

[@howdag711]

Thanks for the great Video!!! I was just a minute away from calling a HVAC company. I came across your video and was able to get my smart thermostat working in 2 minutes!!! Saved a bundle. Thank you!!!

[@RobSomeKnowledge]

Anytime my friend! That’s why I post these videos! I’m glad it could help you out!

[@bhagyeshmohite3123]

This was excellent, plain simple and no runarounds with unnecessary talk. Straight to the point. Thanks a ton and God bless you good man. Keep up the good work.

[@zoomzoomboomboom]

And no music! 👍🏻

[@joshanderson1598]

Your video saved my bacon. I have a 4 wire to my furnace/Thermostat, without a "C" common wire. I needed a 24V wire to run my new WIFI Thermostat. The "24V HUMM" screw on my furnace board was not a 24V hot. But this was and it works great. Thanks man.

[@Rudy-fz1xy]

I really appreciate your help. It was difficult to figure out how to connect the C cable. My ac unit has a connector where all the wires are tied together and were not set up like other units that are labeled specifically with each wire shown. With you're explanation I was able to hook it up and worked great! Thank you!

[@chayden3667]

Of all the videos I watched, this was the one I needed. Best knowledge/insight on where to connect the blue wire at the furnace. Thanks.

[@donjuan8867]

Great video Rob!!! Simple and easy explanation. And no ads to interrupt thank you

[@schpitz101]

Extremely helpful video, thank you! I had been having power issues with my Emerson Sensi for years, but kinda ignored it because the batteries did the job. However, when I wired in my Ecobee 4 it wouldn't turn on. The multimeter showed 0V on the C wire. I opened the side of the air handler and found the C wire, but no control board...just bundles of wires. This is where this video came in! It was so helpful to have somebody explain so clearly the wiring shortcut. After a bit of "jiggery-pokery" I had power to my C-Wire and everything is working great now. Thank you so much!

[@dawnlovejoy4935]

Great video and explanation! I had no trouble with the thermostat side but found the nastiest dust filled furnace. Couldn't find the blue wire because they had cut it so short. Couldn't read any connectors because the dirt and dust. Poor installation of the unit in a small closet and being on a ladder to access. It was all horrible. But your video matched the exact unit and wiring. Got it running in just a few minutes! Thank you so much!

[@vivalageegee]

Thank you!!!!! Straight to the point and explained in plain English! You deserve an award.

[@rocxylemmon8535]

Thanks buddy! My mother is not ac savey and she needs her kids to help her after covid killed our dad so after they got a new ac unit installed, they never installed that c wire so after foing some homework i suspected the blue wire after looking over the schematics but your video just reassured me, after doing your work, the new thermastat came on after flipping the braker back on, now we kids can help our mom with out going over there just for a adjustment. BRO THANK YOU SO MUCH AND GOD BLESS YOU! ❤

[@crystalhenderson8267]

Omg ty! I was getting ready to return my thermostat because I couldn't find a c wire port in the hvac but ur instructions worked!

[@Miguel-pv4ue]

Thank you!!!! This definitely helped me. Lady at homedepot was saying you going to need an electrician. I proved her wrong with your help lol!

[@RobSomeKnowledge]

Haha that’s awesome!

[@mark2213]

Thanks for making this so clear. All the other videos talk about C terminals and additional adaptors. Mine has no circuit board to find a C terminal at. So finding the right ground wire was the trick just like you have shown. Thanks again!

[@applepotamous1376]

Thanks for the video! It saved the day! Kept my family warm tonight

[@T.Ruba_]

3 years old and still gets the job done thank you!

[@RobSomeKnowledge]

Love to hear it! I’m glad it helped you

[@audi_kid]

2022 just got the eco bee 🐝 and had this issue !!! The instructions don’t tell you when you don’t have a panel .. your video was a life saver on that C wire I was like wtf lol but you saved my butt specially trying to do this last minute in TEXAS 85 degrees lol great video !!!!

[@juanjoseestrada6089]

Thank you for your instructional, it was easy to follow an the troubleshot to the point, today i have my new thermostat installed with no previous electric wiring knowledge.

[@Kamkrt]

This was a great help video to get my Wifi Thermostat hooked up.

[@ram6796]

You're videos have bee the most helpful I've found regarding the C wire. Thank you.

[@lewisstephens4807]

Thank you, my setup was almost identical. I was able to get my new thermostat up and running thanks to your video.

[@cdiaem1338]

Man your KNOWLEDGE is PRICELESS, THANK YOU, Thank You, thank you You earned a subscriber

[@jagtheripper5297]

We appreciate people like you doing a selfless act to help others 👍🏻

[@RobSomeKnowledge]

That’s the whole purpose of my channel to help others out and save people some money vs calling someone! I’m glad it helped you out, thanks for the comment, that helps out the channel!!

[@rocxylemmon8535]

I agree!

[@rocxylemmon8535]

​@RobSomeKnowledge im the same way

[@amadorsoto1438]

You made me look like a wizard for my wife. Thank you for your knowledge good sir!

[@RobSomeKnowledge]

Hahah 🧙‍♂️ 👍🏼. Anytime my dude!

[@chilton225]

Great video! So you are essentially connecting the circuit I got it and smart showing you used gloves thanks for all the tips! Struggling to get the cover off the furnace panel now.

[@ArtPolania87]

I've been meaning to access the unit because I have this issue, eating up batteries every 2 weeks. And the c wire wasn't connected to the unit. Thank you very much!👍👍👍💯.

[@markgoodson7720]

Thanks man. Good talk through and straight to the point. Making it easy for those of us that don't know HVAC.🤘

[@RobSomeKnowledge]

No problem I’m glad I could help you out man!!

[@zhaoyun1230]

This saved my day. Thank you! I thought I had to extend the C wire and connect directly to the board.

[@RobSomeKnowledge]

It was quite frustrating for me at first too until I did a bunch of research. I’m glad I was able to help!!!

[@ddog1218]

@@RobSomeKnowledge I tried to wire directly to the c terminal, it did not work, there is a make delay timer hooked to my c terminal and the air compressor, can not get it to work

[@CountryBarbie15]

I don't even need a new thermostat, but I still watched 🤣 always great info!

[@prashanthshanbhag69]

Thank you, I installed Amazon Thermostat and it was not turning on. Voila C-wire was not connected. This helped!

[@Ricardinho101985]

You da man, sir!!!!! Well explained , straight to the point, just what I needed to still my new thermostat. THANK YOU!!

[@samm9017]

Thanks a bunch bro! You saved me $500 as I was able to install it myself. 👍👍

[@RobSomeKnowledge]

Glad to help! Love to help people save some money!

[@gerryjohnson7357]

Thanks for posting this video! Going to upgrade to a new smart thermostat, and this is just what i was looking for.

[@Vluhd]

Thank you! I know nothing about this and you helped me get my new thermostat working!

[@RobSomeKnowledge]

That’s awesome!! Glad I could help ya out

[@ragelikecage4012]

Thanks! Just fixed my "non-working" c wire issue for my upstairs thermo. We got new thermos for both up and down, but for w/e reason the downstairs one already had a c wire connected to the furnace while the upstairs one was wrapped on the wire still. It took longer to get into the attic than it was to just simply attach the c wire where it needed to go. Both thermos are working perfectly, nice to finally have wifi and smart features with them.

[@RobSomeKnowledge]

No problem. I’m glad it could help you out!!

[@brycyncampbell7899]

You saved me a technician fee! Thank you

[@Macgyverjrofficial]

Thank you sooo much !! My system was setup like this with just wires and no labeling. I used the blue wire like in the video and connected to the ground for my AC compressor !!

[@billsheridan8196]

Great video, save my day. Thankfully you had an older unit similar to mine. I just had wires nutted together and no C terminal. Keep up the good work!

[@RobSomeKnowledge]

I’m glad I could help! That’s why I post these videos!!!

[@binyacom]

You rock. Thank you for saving me the cost of having to pay someone. I knew about the common wire but had no idea how to hook it up at my new apartment’s intimidating looking ceiling accessed furnace. Thermostat and A/C low voltage wires were just as you described. My ecobee is reinstalled and back online. 😅

[@chilton225]

It worked!!! Thanks best video I watched on this most helpful thank you.

[@lovetoexplorewithjamieandm477]

This is the exact setup I have in our new condo and this worked perfectly for us. Thank you for the video!

[@dens3096]

AC guys do it for purpose so they can charge you extra cash when you want to install WiFi thermostat 😂

[@rocxylemmon8535]

Thought so! I thought this too but i was like nope! I can do this!

[@getahungebre3291]

My New Google Nest Thermostat is working fine because of this video. You are awesome. Thank you

[@andrewsharp712]

Thank you, the wires were not colored correctly on my furnace, but I was able to figure it out by identifying the ac compressor wires as you suggested!

[@JJohnson467]

Thank You very Rob. Those was very understandable instructions. You saved Me.

[@johnathanharris9387]

Worked like a charm! Excellent video your video was the only one that got the job done. Thanks for posting

[@adno2015]

This video helped me so much! I can't tell you enough how thankful I am!

[@theresarice5947]

Thank you! I have the same issue , your description and video was very helpful! Made my installation of my new thermostat a success!

[@jackstyron7619]

Great job with your help I found the c wire in my air handeler...my ecobee works great again thanks again yours good teacher

[@lancepickle8466]

EXACTLY the video I needed to find! Thanks!

[@samdang5246]

Thanks. This video helps me create a C line.

[@Michael-gg4nq]

This video helped me fix the issue with my thermostat installation. Thank you.

[@cheekss86]

This video helped me install my thermostat correctly. Thanks for your video

[@TKreeps7635]

Thank you very much! Exactly what I needed, great explanation

[@saldesigns257]

Great video! it was helpful in my situation. Keep up the great work!

[@1Fine69c]

DUDE thank you. i was dealing with this same problem today. Had to sub to the channel for this one.

[@Turrence]

Thank you! This video was very helpful.

[@1kennyroberts]

Because this video was so helpful not only did I liked it... I subscribed to the channel

[@RobSomeKnowledge]

Thank you, that means the world to me!!!

[@agredo]

THIS video REALLY help me out !!! thanks man !!!!!!!

[@AdelaCarvajalRealtor]

Thank you. We did it. Great explanation 🙏🏼🙏🏼🙏🏼🎉

[@AndresGomez-ey6lh]

This video saved me money 👍

[@1Brain4Wheels]

Very good video, I’m going to try and tackle this project next weekend - this is extremely helpful! :)

[@blanejohnson6294]

Perfect Explanation! Thanks!

[@judevecoli865]

Thanks for this. I'm still trying to find the control wires inside my HVAC unit. But now I know what to do once I get in.

[@luluguzman6782]

Thanks for your help. It’s great description

[@Bill-tb3kx]

Excellent video! It was perfect and solved my problem exactly - Thank you!

[@ef2744]

Excellent explanation. Thank you.

[@darvinmcclellan5070]

you made it look "easy peasy"...I hope. I opened up my furnace/ac and thought, "oh my gosh, where do I go from here!"

[@RebelliousArrow]

Would it be any different if you have gas heating? And thank you for the video it is a great help and explains everything!

[@NO-END]

I have gas furnace and I did the exact same thing he showed in video. I already solved it but I wish I saw this video first would have made it so much easier for me. thumbs up

[@austinuhri]

The video was very nice but it would have been nice at the end of the video to see you verify the wire voltage, for the blue wire, at the thermostat with a volt meter.

[@rocxylemmon8535]

Yeah! I tried at first to get a reading but none was on it, i assure you it's there though lol! Has to do with being a seiers circuit.

[@njboesman]

this is great and probably works in 90% of applications, but here in the northeast, we have gas boilers and baseboard heat which means no control board at the boiler(instead we have an Aquastat). In my application, the smart thermostat will be controlling both the heat and the AC (R1&C used). I have extra wires (3) coming to the thermostat and a 24v transformer near by boiler, the question is where to connect the 24v to the device?

[@ShirleyAerial]

This worked for me and my Amazon Smart Thermostat. My system was older and it just appeared the C wire from AC unit went to a ground. But that ground was all I needed to make it work in that junction the AC wire nut connected to.

[@mikelove5119]

This helped me out a lot man appreciate the video

[@crotopoc]

Another excellent video!

[@drumbyte]

Great job explaining it!

[@danielpedroza5277]

This helped so much. Thanks!

[@hectorreyes2167]

Thanks! Your video really helped me.

[@RobSomeKnowledge]

You’re welcome I’m glad it helps!!

[@OswaldSoans]

thanks rob very interesting do you have anything on a messed up wiring in a UL-KFR71V/X , so i can get me back up running ? I am new but understand low power and high power wiring safety

[@RobSomeKnowledge]

Sorry but I don't unfortunately, I don't specialize in HVAC but just made this video with all the research I did on my specific system, to help others with similar system. You may have some better luck asking that question with a more specialized channel that focuses only on HVAC content.

[@SharkeyBrawler]

Video saved me. Thank you soo much!

[@DanStratocaster1]

Excellent. The only thing I would add is that it’s better to wrap that thin blue wire around the other bundle a few times to secure it better before you wrap the copper ends together

[@RobSomeKnowledge]

Ahhh good tip!

[@coparaji4616]

Thank you, Now i can finish my wyze install

[@RobSomeKnowledge]

Glad I could help out!

[@tedlahm5740]

Will no longer need the batteries in the new thermostat? No mention as to why we are connecting the C wire? thank you

[@RobSomeKnowledge]

Yes that is correct.

[@GreenSculptures-Abhi]

Thank you , thank you, thank you❤❤

[@iankz4144]

Thanks man. You saved me a lot of money🤩🤩

[@selectscents]

Going to try this tomorrow. I have the unused c-wire behind the old thermostat but I have to find where the furnace covering is to check if the unused c wire from the thermostat is connected there or beung used at all. I haven't been in this house long in Texas and it might be in my attic. Can I just try and connect the unused c wire to the new thermostat to see if it will power on? Basically do you think the unused c wire is connected at the furnace already???

[@selectscents]

Your video seems extremely helpful btw!

[@RobSomeKnowledge]

Im glad you found it helpful. I mean you COULD try to just connect it, but I would really recommend just finding the furnace/air handler and actually checking. More than likely its not connected anyway if it wasn't connected at the thermostat. There is a possibility you could short something out if that isn't actually a c wire. Just take the time to go find it and verify the wires.

[@selectscents]

Don't know if you have the answer to this butttt, it worked but it didn't. I bought a $70 honeywell thermostat that required the c wire and this is the one I installed. I found the c wire by the motherboard of the furnace, attached it and went to turn the power on at the breaker box. The air came on blowing cold but I had no screen on the brand thermostat. So I couldn't control the temperature or anything. It literally just stayed on all night. Going to return the thermostat today because I feel like it might be a defective unit. Thoughts.

[@RobSomeKnowledge]

Where exactly did you attach the wire to?

[@selectscents]

@@RobSomeKnowledge so I got it squared away but I had to call an emergency AC tech out. Great Info I learned. He told me that the existing unused c-wire ordinarily should work but in some cases it's a reason why it was not used ( like it could of been defective). Check this out though.....when he came into my house he asked to see the old thermostat which was battery operated. I don't know if I told you that the first thing I did was swap brand new batteries into it when I saw the screen was blank when I came home last Thursday. I noticed the last batterie connection had a LOT of corrosion. I scraped it off, popped in 3 new batteries and the thermostat did not come back on. When the technician came, he opened up the original thermostat, put the new batteries in too, but before he popped the batteries in he said, " don't tell anybody I showed you this". He stated that over time the metal prongs on the top and bottom of the batteries can get stretched out and not touch the batteries once vertical on the wall. He squeezed the 3 sets of 2 prongs together for the batteries and the old/legacy/original thermostat came right on!!!!!! I never even needed a thermostat! He said this happens on 2 out 10 house calls!!!

[@justdissin7340]

Hi rob. I have a central air system which doesnt have a C terminal on it, it does gave a ground terminal though. Would i be able to use blue wire & connect to that ground terminal? Or just connect to screw on cabinet?

[@ror3999]

love the name of channel

[@RobSomeKnowledge]

hahah thanks!!

[@musicmaker33933]

I have this same problem where the C wire is too short to reach the HVAC terminal, but the wire already going to the C terminal (and also the Y terminal) doesn’t look like it’s going to the thermostat. (Possibly the compressor?) and isn’t spliced at all. Could I just buy some extra thermostat wire and extend that short C wire to the terminal?

[@tristansteiner6727]

Incredible channel. You're legend

[@kenwarner5387]

great video! very helpful