HVAC Furnace Has No C Terminal?
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- čas přidán 5. 06. 2021
- Does your HVAC furnace not have a low voltage 24v C terminal? If you are looking for your 24v common in the furnace and not having any luck finding it, there are 2 easy ways you can try to track it down. The first one is to trace the 24v common wire from the transformer and see where it goes. Wherever that wire hooks up to, will be a 24v common terminal. The second way is only possible if you have central air. Find the thermostat wire coming from your air conditioner and trace where the white wire goes. In almost all cases it is the white wire that is the common. The Y wire (red) should go to a terminal that is obviously marked as Y. If you trace the white wire, that will also lead you to a 24v common terminal. Hope that helps!
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#wordofadvicetv #commonwire #furnacecommonterminal #commonterminal #hvac
Thanks for explaining what ALL THE OTHER videos could not and did not. I am referring to the lack of a C-Common wire when there is no control board. Your explination helped. Thanks.
Thanks! My heat went out and I bought a new thermostat. The new thermostat needed the C wire. But my old furnace didn't use it either. I followed your steps to find the common and hook up my furnace to my new thermostat. All working now and no repair man! Huge thank you again.
Dude, great explanation! This answered my main question and a few others so I didn't have to go looking for those answers separately. You earned a new subscriber.
Thank you very much for posting this video! It took a lot of testing in an extremely tight space but I found the 24vac source. Yayyyy!!!
Thanks this was very helpful. Got my wireless thermostat running today cause of you! You're the man.
thx for makingand sharing this! just like all your other videos, this is extremely helpful and you did a fantastic job explaining!
Wow. Amazing video! So much more helpful than any other video I’ve found. I thought it was me being crazy, but turns out my apartment furnace is so ancient, it doesn’t have the control board i’ve been looking for. With your video, I can finally finish this thermostat installation :).
A great video. I shall try to find my common tomorrow. Many Thanks!
Thank you for this!!!! You my friend know what he is talking about!!! I found my common because of your video!!!👍🏾👍🏾👍🏾👍🏾👍🏾👍🏾💯💯💯💯💯💯💯💯💯
Always find your videos when looking for refreshing my memory on my own ac. Today I am going to go with a wireless thermostat and don't have the common which it requires. Luckily I have five wires and will simply connect the common to the board and thermostats c. Sounds too simple. But I like. 👍
Great video. New Wi-Fi thermostat is working thanks in a large part to your instruction. It gave me the confidence to give it a try. Many THANKS..👏👍👍
Hi Jay, it’s all about the 24 vac! Glad to see your back producing great YT videos!, Aloha!
Great detail bro. Good tech ✌🏼 I’m learning from you
Helped A LOT!!
My hvac experience is limited, but I know a lot of the newer thermostats have to be supplied with a C wire to work properly and I always assumed that as a last resort that the common could be taken off the chassy or tap into the common from the transformer. Thx for confirming it. Great video!!
I have the same situation, and my furnace company told me that the green wire cannot be connected to the furnace. So unless them some other device that can be used as an extender I’m not able to get a thermostat that can be used within an app. I’ve watched so many videos, and I’m ready to give up.
@@AnnD2023 Don't give up entirely, I'm in the same boat and discovered a device on Amazon called "Common Maker" that uses a transmitter and receiver to achieve adding a C wire.
I really appreciate you for your video. Very useful for me. Thank you
I love your videos !!!! Thanks Jay
Glad you like them! Thanks for stopping by Joey! 😄
Love all your videos. The steps are so clear and easy to follow. One request, if all possible, could you please put together a video on how to install Emerson Comfort Alert diagnose module? Thank you much!
Great video, thank you.
Great instructional videos. I've saved a lot of money by following your troubleshooting tips and maintenance procedures for my furnace and air conditioner. Thank you so much.
Has anyone ever commented that you look and sound a lot like Chris Hayes on MSNBC? It's kind of uncanny. 🤣
Love how you make complex things seem easy. Thank you for your videos!
Glad you like them! Thank you for stopping by!
you're a genius! because even I'm an electrician, I couldn't get it. Lol
Your video just helped me identify a splice (blue/yellow). I ran an extra wire to get a com for my new thermostat. Didnt have a 5th wire ran to my old wall unit. Thanks a bunch!
😢😢😢😢😢😢😢. 😢😢😢😢😢😢😢😢😢😢😢😢😢😢😢😢😢😢😢😢😢
Great vid! Thanks man. I was about to return my new Wi-Fi thermostat if it wasn’t for your expertise.
Poor kid.
Three sisters age 92, 94 and 96 live together in a house. The 96 year old draws a bath. She puts one foot in the tub and stops and yells to the others, hey was I getting in the tub or out? The 94 year old yells, I don't know, I'll come up and check. She starts up the stairs and stops and yells was I going up the stairs or down? The 92 year old shakes her head and says, boy, I hope I never get as forgetful as those two. She knocks on the wood table for good measure. She yells I'll be up to help you both after I see who's at the door....
Ba dump bump...
LOL nice
Haha thanks Mr. Classic! I will need to use that one 😄 and if anyone else has good ending material for me, I am all ears 😉
Question, if you have a video please point me in that direction. Say I want to hook up a pan shut off switch how is that beat accomplished. I heard you interupt the compressor and allow the fan to keep running, and I've heard interupt where the compressor and fan shut off? Basically how do you wire that in. As a follow up, how should you wire in these new air cleaners to operate while the fan is running. Thanks for some great education.
Always on point, thanks Jay.
Thank you! Good to have you here Hercules! Stay cool man! ❄😎
@@WordofAdviceTV same to you.
another good video, keep em coming.
Thank you good sir! 🙂
thanks for the video. ithis was the solution i was looking flor.
Thank you again!
Muy buena la informacion...
Thank you so much. I just fixed a problem with my ecobee4.
another great video
Thank you Jeff! You are a great man! 💪💪
You deserve a thousand likes💯👍👏
Create 1k accounts 👍
Haha I appreciate the thought! Thank you!
I know some smart people stop by my channel sometimes so a question for you 😃 Besides tracing the 24v common wire from the transformer or from the air conditioner, what other ways are there to locate where the 24v common terminal is in the furnace? Or is there an even better way to do this?
I think I'm a smart person - I bypass the fuse and short each power wire to ground with the door safety switch depressed. Whichever lets the magic transformer smoke out is the one that is not the common. Then I refill the transformer with magic smoke, and also leave the fuse bypassed to save the next guy the extra step of doing so when he needs to find the common.
Thank you very much . You saved me a $75 service call . I had to light my pilot light in the attic and im 350lbs that was fun to get up there first of all . Then I have to lay in the crawl space . We'll i got the light lite but my fat a*s belly pulled on the white wire and it came undone I didn't know where it went back to. Your video helped me understand it. Got it back in place where it said "w" big dummy. Heat kicked on and I have a back ache but it works. .. thank you much
Thank you so much
THANK YOU!
i cant find the control board. i have older weil mclain cg boiler and i want to install a nest and need to install the C wire. can you do a vid on where to do this on a boiler (heat only) that doesnt have a control board? or point me in the right direction so i know where to look etc. all advice is appreciated.
Question for you, my wires look like yours coming in to the furnace, the blue and tan wires are unused wrapped around the other wires, same as the thermostat wires, BUT I tested both the blue and tan wires for voltage, the blue has 10v and the tan wire has 11 v evin though they are not hooked up in the furnace or the thermostat??? I'm confused
The comm wire sheered off on the furnace side and the thermostat went out but it was a super easy fix cause I can see where the piece of broken wire was on the board just had to strip a little bit off to expose the wire and stick it back on the common screw on the board. They tightened that screw so tight that the wire just sheered off lol. Super easy fix thanks for the vid.
Glad to hear you were able to find and fix the problem! Stay warm!
Thx, It help me
Great Videos!! I have learned a lot. I am having a weird problem where my thermostat was going blank and then later in the night it would come back on and it would run until the AC until next day when it got hot again and shut down. I have 120 volts going to the furnace, The 3 amp fuse is good on the board , I am thinking it might be the 24 volt transformer is getting to hot and shutting down, in turn not putting out the 24 v needed to turn on the Thermostat. What is the chance it is the board. I am picking up the transformer on my way home. Thank you!
Great video buddy glad to see you bad 👍👍
Thank you T&T! Hope all is well on your side of the country! Stay cool and have a kicka** week! 😄
FINALY. I was kinda assuming grounding to the chassis would work, but all i could find was articles on how to add a c wire, but nothing about what to do if you have no c terminal...
Brilliant video. I was wondering what the red (connected with a yellow wire in the Y block) and white wire (actually its a second white, connects to the C terminal) were. This explains that they come from AC unit and it makes perfect sense. Thx!
Great explanation. I have one question. I have a heat pump system and want to install a Nest thermostat that requires a C wire, which I don't have. I'm seeing some folks pull the green (fan) wire and instead connect it to the C on the thermostat and at the blower. Since I never run the fan separately this seems like a good choice. Does this make sense? Pulling wires would be ideal but almost impossible since I think they stapled the wire to 2x4 studs. Thank you.
Thanks again
Always welcome! Thanks for stopping by!
Thanks!
I have an old furnace with no ac. There are 2 wires to the t stat. I have a smart t stat that needs a common. What’s weird is the transformer is ungrounded so when i check the secondary voltage its 13 volts to ground each side but 26 across the secondary. Do I change out the transformer to a grounded one and then use the a screw for my common.
Do you know what gauge wire comes off the harness of those control boards? Also, what gauge wires comes off the blower motor?
In this video you show connecting a wire directly the metal AC case. Does the other end of the wire connect to the Thermostat "C" terminal to complete the "C" wire connection? Thanks! Clint
Thanks sir..
Thank you
You're welcome Mr. Welch! Thank you for stopping by and have one heck of a fantastic new week!
Thanks. You helped me get my Honeywell 9000 hooked up. There was a Blue wire coming from the wall connected to the old Battery operated thermostat but it wasn't hooked up at the furnace. That White & Red coming from the AC did the trick on where to connect the Blue wire. I recently moved and took my Honeywell with me. I like it too much to have left it. Especially at a $130.00 then and $180.00 now.
@GLC, did you plug that blue wire from thermostat into C connector on the controller-furnace, where your White wire was already plugged in and did you end up with 2 wires on C now? (blue from thermostat and White from AC outside) and did you need the blue wire plugged in to provide power to your thermostat?
Welcome back
Hi Jay, I have a question, what does it mean if I'm not getting voltage to w but y and g are
Love the jokes !! Thanks, Jay.
so if i can't locate the C wire on my Rheem unit can i just attach the C wire from the thermostat to the body frame?
Very helpful video. One question if my control board does not have a C terminal. Can I simply connect a thermostat C wire to the C wire coming directly out of the transformer to provide power for the thermostat or will this cause issues?
May I ask, my home only have gas heater, with 4 zoning. (AC units in each room) do I need to connect 4 individual C wire between the panel's wire to the thermostat wire?
how do you match the wires on the green block to a thermostat that has L1 N1 N and L thanks
Great Video. I have a really old i.e. 1980 roof top HVAC system. I looked inside the HVAC unit and could not find a control board. I did see a really old transformer and an Ignition control unit. Any way how I can find the C - Wire?
I was testing the the square box with a fork and it knocked me out. I can’t remember what happened. Should I retest with the fork?
thanks for the video. Could yu consider make a video o how to connect the humidifier on the nest thermostat please? thanks again
Great videos, I've learned a lot! Quick question : My furnace breaker immediately trips (kicks back) when I try to reset it. What should be my steps? I've looked for a wire short indoor and out and dont see anything abnormal. Should I replace breaker? Thanks for your help
Did you replace breaker? What was the solution? Sounds like a shorted wire to me. I had a wire go bare from rubbing on a pipe vibration; but it blew the main fuse as I recall.
Thanks for information. I have only five wires coming out into the thermostat. I don’t remember exactly which one that I had to disconnect for it to start calling when I have all wires connected to the thermostat. It doesn’t cool down. Just keep some running. What am I doing wrong
What happens if o screw common into chasis and is the chasis as a common to the outdoor condenser since I only have one wire left on my low voltage ?
thanks for the helpful video. my furnace has a Honeywell R7284 Oil Primary Controller that the red and white wires connect to. There is no air conditioning or other equipment attached to the furnace. the white wire is connected to the T terminal and the red one to the T3 terminal. Then there are 3 terminals next to those that are numbered 3, 2, and 1. Would one of these be the C terminal? how would I know? Would I put a probe on where the red wire is hooked to, then look for 27 volts on one of the other unused terminals?
Here's an odd one for you. I have a GE Vertical ZoneLine PTAC, when I'm testing the 24v terminal strip I get 24V on most of the terminals, when there's no wires connected, measuring from each terminal screw to ground. I found 24v on R, W, Y, B, C, and some of the other more obscure terminals. Is my board bad? Or am I measuring something wrong? Tenant's complaint is that it runs forever and electricity bill is high. It's a heat pump with aux electric backup and I'm wondering if the unit is messing it up. Compresser runs fine on AC, Heat coils near top of unit got hot last time I did an open test call for heat. The unit wants a heat call on W, not Y with Elec/Aux on W. The manual says 'unit will decide whether it needs to use heat pump or elec/aux'. It does want to receive a constant B signal when heat mode is on.
Thank you! You helped me figure out how to replace my old analog thermostat with a smart one without having to spend 300 on an "expert" 😅
I'm trying to do the same, but having trouble. My wire coming from outside is like the one in the video with a bunch of wires. But my furnace also doesn't have the control board. All wires are hooked up by twist connectors. The blue one connects to a bigger black wire like the one you call a 120v from the transformer. Those four bigger wires are red, white, black and green The present thermostat has five wires but no "c". There is an "o" for the heat pump I think. The red, white and green wires from the thermostat connect to the corresponding bigger wires. Then the blue wire from the outside bundle to the black one. What the heck?
thank for the video...now I can go install my Google Nest thermostat.....
thanks , i just wish i could just run fan only sometimes , i have a honeywell wireless t stat ,love ure videos!!!
Ah and I suppose that thermostat does not have a fan only option huh? Some of these new thermostats are inconvenient like that.. 😑 And thank you! Happy to hear you love the videos!
@@WordofAdviceTV ure probably correct , keep up the awesome work!
I don’t have a C terminal, only wiring harnesses. Can I cut and splice onto the 24v common from the secondary side of the transformer in order to obtain the common that I need?
I'm trying to connect the C wire from thermostat at the furnace end to the correct wire. There is no terminal block or control board with marking, just bunch of wires.I have the brown from condenser with two leads.1. White wire connecting to Yellow on Thermostat wire (Y). 2. Red wire connecting to a blue wire that goes to the steel frame of furnace board. My guess is red wire is the C wire in my case and need to connect thermostat C wire with that. Did I identify C wire correctly since it goes to the frame?
Hi Jay, I have an old Lennox furnace from the 90’s and it does not have a c terminal. I am installing a Honeywell smart thermostat requiring a c terminal. When I follow the 2 wire from the A/C unit outside to the furnace the red wire goes to the “R” terminal on the furnace panel but the white wire does not connect to the furnace panel it is connected with the yellow wire from the thermostat cable of wires with a wire nut. Does that mean the common can be achieve by connecting into the white and yellow wires that are in the wire nut? In the thermostat bundle of wires is an unused blue wire that is not connected at either end. I was planning to use that blue wire as my c wire. Can I connect that blue wire into the wire nut bundle I mentioned and then connect the blue wire to the “c” on the smart thermostat?
Do some furnace units have AC built in. Without using outside HVAC unit?
Great Advice Jay and dare I say ... That joke had a ''crappy '' ending ... Lol ...
Lol, thanks Eddy! I appreciate you stopping by! Have a fantastic week good sir! 👍🤙💪👌
Love you videos, so helpful. I hope you can advise me. I have a blue common wire unattached. However, all of the 5 screw in slots on Amana furnace control boards are full including the common spot where there is a red wire. Where would I attach the blue wire. Grateful for any help.
P.S. Trying to install a nest thermostat.
Hey....I know you're specialty is central units, but I thought you could give me a word of advice for my portable unit.
Maybe you can help me. I've got a Haier portable. I was neglectful, and didn't realize there were two sets of fins, when I took the back off, the bottom fins were caked with dirt. Before that, the compressor made a racket, so I turned it off. I cleaned everything with a hose that let it sit in the sun a couple of days. When I tried it again, the compressor immediately kicked in quietly and blew cool...not cold air, but then kicked off after a couple minutes. Started a couple minutes later again but kicked off even quicker. The compressor gets slightly louder right before it kicks off, but nothing like before I cleaned it. Do you have any suggestions?
Great video. Very helpful..... and I listened right to the end... which presented me with the need to change my diaper!! Too funny you are!!
I have Agro AZ-6P zone controller and 4 zones hot water base board heat with 4 thermostats. My controller does not have anywhere “C” terminal. All of my 4 thermostats have two wires ( Red connected to R terminal and White wire connected to W terminal). I have a spare 24 v transformer near the control board. There are unused wires in the TT wires. My question is that can I connect two wires from this spare transformer to two unused wires in each TT wire to supply 24 v to each TT?
My furnace only has an R, G, W terminal. However the chassis of the furnace is grounded to the 24 V side of the transformer. Is it okay to use the chassis as common terminal for a smart thermostat?
Thank You! So I'm curious. Your saying. I could hook up my smart thermostat C wire on the furnace body ground wire?
Yes. I've seen that done plenty of times before and seems to work just fine.
I have the weirdest question. I have a weil mclain cg boiler. According to the schematic, my thermostat goes from r to g instead of r to w. I got my nest thermostat to work by hooking red to g on the boiler and white to red on the boiler. and c to c. If I hook w to g and r to r, it doesn't like that. Would I be better resetting the nest and telling it I use 4 wires instead of 3 and running g to g and adding a white wire to W on the furnace?
Quick question. I have a c wire not being used but, now I’m going to install a smart wifi thermostat and I need to wire that c wire. Easy at the thermostat but, at the furnace there’s already two wires connected to the c location. Where do I connect the c wire now?
The cable to my home thermostat has 4 wires, there is no spare wire. It's not practical to replace the cable with new one having 5 or more wires. What would you recommend for installing a smart thermostat?
Hi Jay I am installing a new no battery operated thermostat and I’m have an issue. My ac is a package unit Bryant and I’m trying to add the common wire
From the condenser board I get 23-24 volts but when I check down stairs I get 16-18 volts and does not turn on my new Venstar thermostat. I tried using another extra wire to see maybe the brown common wire was shorted out but I got the same with the extra green wire 16-18 volts. Am I missing something? Also I’m checking from Red to green/brown Common terminal.. thanks
Hello, the common contact on the circuit board is only pulling 22.5 volts, every other is 28 volts. This is preventing the fan from operating. Can I tie in the A/C condenser neutral wire with another low voltage wire in the furnace? This video is a great explanation to find it, but where could I tie in aside from the terminal?
Thank you sir
I purchased a honeywell C Adapter for my Alexa thermostat. I have W, W2, Y R, G and B terminals. The B terminal is where the A/C common connects to. If I use that for my C, the thermostat will activate both the furnace and A/C. Thoughts?
Good morning. If the is a zone panel. And i have 3 thermostats going into it. How do I add a c wire to all of them? Do o need to run a blue wire from the furnace to the zone panel then in the c terminal of the zone panel plug all 3 blue wires together?
Thanks for the video. Have some questions
I installed a nest thermostat and looks like NEST has a battery in it that needs to charge and it is not getting enough juice to it and shows low battery. I traced the brown NEST thermostat cable from NEST to the furnace unit in basement, the Nest thermostat cable plugs into a controller (The general 90, model 50A50-110), I notice that only (Y, W, R, G) are connected to the controller from NEST thermostat cable.
I also Notice that there is another brown cable (similar to NEST thermostat cable), that seems to be going outside the house, this cable also plugs into the same controller (The general 90, model 50A50-110) in the furnace, but it only has 2 wires plugging in (Y and C), in the Y the RED wire is plugged in and in C the White wire is plugged in.
My question is, to give power to the NEST Thermostat, can I plug in the blue wire from my NEST thermostat cable (blue wire is not connected to controller right now) into the C connector on the controller (The general 90, model 50A50-110), Keep in mind that the C connector on the controller already has a white wire connected from the unit outside, so I will be connecting a second wire to the C connector and the connector will end up with 2 wires a White wire (going to the unit outside the house) and blue wire (going to the NEST thermostat).
First, connecting blue to the C connector on controller, is it going to give power to my NEST?
Second, Will this cause any issue with the unit outside, since C will have 2 wires now?
Third, What is the C connector for ?
Lot of info, thank you for help. hopefully this all makes sense.
Hey my air conditioner works fine on the outside but in my attic it cuts on and off every five minutes do you think I have a bad circuit board
I went from the 24 V on the contactor coil in the condensing unit to the frame and blew my transformer please explain
Very good and helpful video.
Quick question, my oil furnace model: CMF2 80 PO CONVI have 2 wires going to my old thermostat, I will buy a nest Thermostat and I am not sure if this model of furnace have a C wire. Can you tell? If it doesn’t have a C wire am be able to add one?
Thank you
wtf.. Did you even watch the video? You best hire a pro Laddy.
Thank you for the great video. I learn a lot from your video. I saw the smaller transformer on the left of the voltage transformer. Can you tell me what is that use for?
You're welcome! Glad to hear you learn a lot. That smaller transformer is actually not originally part of the furnace. That small transformer is solely for the bypass humidifier which is installed in the ductwork behind the furnace.
Hi jay tranks very much for your videos... you explanation its great!!! I have a question in the furnace if The technician in the call found the correct 24 volts at all points in the control circuitry where needed. One component is not functioning, preventing the flow of gas to the pilot burner. What is it? What did you think the component is fault?the ignitor is OK and sparking, but there's no gas to ignite,so what could be preventing it for lighting? What component is at fault?
I would start by seeing if the control board is blinking any error codes after it fails to ignite. If you have an ignition module instead of a control board, those tend to fail and not send power to the gas valve. If your ignitor is sparking, the next thing that should happen is the gas valve gets energized. So I would check to see if the gas valve is getting 24-27 volts. If it is not, then there is a good chance that the board or ignition module is bad and needs to be replaced. But if the gas valve is getting power then either the gas is turned off somewhere or the switch on the gas valve is switched to off. If you verified that the gas shut off valves and switch are both on/open and it is getting voltage then I would say that the gas valve is stuck in the closed position and should be replaced.
Another possibility is that the gas orifice on a burner or two are plugged and not allowing the gas to flow through (especially the burner in front of the ignitor). If you have an intermittent pilot then the little pilot orifice (tiny hole where the gas comes out from on the ignitor pilot assembly) may be plugged and needs to be cleared out.
But keep in mind that this is only my guesses, since I am not there to see it I can't say for sure what is going on. I hope this gave you some ideas of what to take a look at though. Good luck!
I do not have a control board so what wire go where form condenser
I am so glad that you post this video. I have been struggling with a air handler with no control board. A more than 30 year old air handler (Lennox CH19-65-2 and B19-51-1P) and a condensing unit (Lennox HS19-651V-2P). I guessed it to connect the C wire from an ecobee thermostat to one of the two wires from the condensing unit. I probably connected the C wire to the hot wire instead of the common wire. Would this damage the machine? If so, how do I do troubleshooting? As it has no control board, I couldn't find a fuse or anything. Any comments will be very much appreciated. Thanks! I have learned so much from your videos!
Happy to hear that the video was timely for you! From what you explained, it sounds like you wired a direct short. My guess would be that the thermostat would get damaged first. But did you disconnect it right away? It's possible there was no damage but of course I can't say anything for sure without being there. I should have explained this better in the video but if you have a meter it is very easy to determine which wire from the AC is hot and which is common. Simply measure voltage from one of the terminals (C or Y) and put the other lead to any ground terminal or even a screw in the furnace. If there is 27v, that is the hot wire. If no voltage, that is the common. This troubleshooting would be done with the furnace and AC powered on and on standby. (not running) And if there is a door switch, that needs to be closed too. Sorry, that was a long-winded answer. Let me know if that made sense 😅
It looks like the thermostat is still ok so I will try to connect it to the correct C wire as shown in your video. However, I will have to clean the condensing unit first because I found it has become a bee's nest when I opened it. It looks like the compressor was wrapped with material something like the batt for attic insulation and it became the home for bumblebees! I am wondering why the previous owner of the house did that. Any reasons to insulate the compressor itself? I live in Boston btw. Thanks!
Something to add here! If I remember correctly, the thermostat lit up when I connected the wire but it doesn't start the air handler or condensing unit when I set it to cool and dropped the temperature. Maybe I didn't connect the wrong wire? In addition, I tried to jump start the air handler by connecting R and G "binding posts" with a wire. The air handler didn't start but I heard a zap and maybe some spark. Or I can only do this on the thermostat side instead of the air handler side?
We have a 20 year old Goodman furnace. It does not have a C terminal - however there is already an unused C wire running from our old thermostat. We are installing a Nest smart thermostat. Where do we attach the C wire at the FURNACE? (There is no c terminal to simply plug it into). Can we attach the C wire to the ground that runs from the 24v transformer? No one seems to have a clear answer how to install these thermostats with a furnace that has no C terminal. Thanks!
That's exactly where I'm at, hopefully he responds.
I have found myself in this exact same situation with a house I just purchased. Any luck?
Probably need to go with the last ditch effort and ground it to the frame
I can confirm connecting the C-wire to the my transformer 24v side (opposite of red wire) worked for me and in the process determined that my fan relay coil was burned out which is what got me searching around the unit in the first place
Hi there! I am in a similar situation with an old Goodman GDT070-3. No C-wire at thermostat or C terminal on the control board. The Nest compatibility checker instructed me to get the power connector, which I have. It looks like my best option right now is to ground the C wire coming from the power connector, but in other forms I've read that a ground is not appropriate. I'm curious about how you resolved your issue? Thanks!
What's the situation if there's an old furnace with no control bord and I need to hook up an ac system to it .how did I use the R and the C to it.tnx
Remember an outdoor unit for a heat pump will have many more wires. R W Y O and C and sometimes G.
Thank you for pointing that out! I should have talked about that. As far as I recall most heat pumps do have the blue wire for common though. Hopefully I was right about that claim.
Question... My motherboard doesn't have a connection for the Blue common wire. I have the wire that runs from inside the house to the furnace outside. However, there's no spot on the electronic motherboard to connect it too. Any ideas on how I can get my Nest thermostat to work without buying a wall plug. Thanks