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Old 10-16-2012, 02:22 AM   #1
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New thermostat with no 'C' wire


I bought a new Filtrete Thermostat today and ran into an issue before installation. It has Wifi and I understand that it requires a common wire to power it. My current thermostat is using only W, Y, G, and R.

Is this something that I could add my self? I'm pretty comfortable snaking wires through walls and I've already found the point where everything is connected at my furnace. How hard would it be to run a new wire up to it or run a new 5-conductor line?

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Last edited by mentalcase; 10-16-2012 at 02:25 AM.
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Old 10-16-2012, 06:00 AM   #2
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New thermostat with no 'C' wire


If you have an extra wire in the cable then it should be easy. If you need to run new cable then we have no idea how hard it will be to run new without being there. http://www.venstar.com/Thermostats/ACC0410/

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Old 10-16-2012, 08:44 AM   #3
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New thermostat with no 'C' wire


Really depends on if they stapled the original wire to the studs, when they pulled it up the wall. Only way to know, is to mark the wires, tie something to the end, or attach the new wiring, and start pulling back to the furnace.

Should take you no more than 5 maybe 10 minutes tops to do the pulling, a total 20 minutes to finish the job.
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Old 10-16-2012, 11:26 AM   #4
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New thermostat with no 'C' wire


I am having the same problem. I am under the impression that professionals do not know a lot about this because wireless thermostats are a fairly new thing. I know my local furnace guy could offer only very vauge advice.
I would suggest you search u tube for C wire issue (or similar).
The three choices you have are to jumper the green wire at the furnace control board, hook up a new single wire to the C connector on the furnace logic board or buy a 24 volt transformer as an add on. Utube offers more detailed instructions for these procedures. Obviously it requires you find the furnace logic board after turning of power.
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Old 10-16-2012, 11:44 AM   #5
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New thermostat with no 'C' wire


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Originally Posted by brunetmj View Post
I am having the same problem. I am under the impression that professionals do not know a lot about this because wireless thermostats are a fairly new thing. I know my local furnace guy could offer only very vauge advice.
I would suggest you search u tube for C wire issue (or similar).
The three choices you have are to jumper the green wire at the furnace control board, hook up a new single wire to the C connector on the furnace logic board or buy a 24 volt transformer as an add on. Utube offers more detailed instructions for these procedures. Obviously it requires you find the furnace logic board after turning of power.
Adding on another transformer would still require him to run another thermostat wire.
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Old 10-16-2012, 12:23 PM   #6
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New thermostat with no 'C' wire


Notice how I referenced the u tube videos to get greater detail.
I did this to shorten my prescription . Obviously , for example , I left out that before jumping a green wire the logic board still needs to be checked to ascertain what color wire is being used on what terminal. The concept of an add on transformer involves the use of a new wire but does not involve a wire from the furnace. Remember the whole idea is to give the thermostat constant 24 volt power to run the wireless. It dosent care where that 24 volts come from. Again the videos give far greater details.
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Old 10-16-2012, 01:08 PM   #7
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New thermostat with no 'C' wire


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Originally Posted by brunetmj View Post
Notice how I referenced the u tube videos to get greater detail.
I did this to shorten my prescription . Obviously , for example , I left out that before jumping a green wire the logic board still needs to be checked to ascertain what color wire is being used on what terminal. The concept of an add on transformer involves the use of a new wire but does not involve a wire from the furnace. Remember the whole idea is to give the thermostat constant 24 volt power to run the wireless. It dosent care where that 24 volts come from. Again the videos give far greater details.

No, it doesn't care. It just won't run either the A/C or the heat.

last i knew it only has an RH and an RC, no R terminal, unless I'm thinking of the wrong thermostat.

24 volts must come from either the heating or cooling equipment.

He's better off just running a new wire from the furnace, or using an add a wire.
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Old 10-16-2012, 02:11 PM   #8
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New thermostat with no 'C' wire


Your probably right about the best way. I just included the independent 24 volt source because one of the videos shows a detailed way of hooking that up. It would not be my choice either . Since he has an existing green wire at the thermostat the jumper method might work well for him, assumming the green is the fan power. There is a good video on that method. Since I only have a two wire ( red/white) system I personally will run new wires and just add the common wire at the logic board. Again I am not advocating any particular method because much depends on the posters comfort level and experience .
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Old 10-16-2012, 04:15 PM   #9
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New thermostat with no 'C' wire


I'm fine with running new wires as I do not want anything showing under or around the thermostat. Wire are my biggest annoyance and I'll go through anything to make sure they are hidden behind a wall. I believe the common wire is just to run the wireless so I don't think it matters where is comes from, but I think I'm better off buying some new wire and running it downstairs.

My furnace is not too, too old . Should it have a 24v source that I can use? I'm heading downstairs now to investigate and take some pictures as well.

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Old 10-16-2012, 04:56 PM   #10
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New thermostat with no 'C' wire


Alright. So things look easier then I thought. 5 conductor wire is actually run from my furnace and joins what looks like telephone (4 conductor) wire via wire nuts. Then it is run up to the t-stat. I have a big whole directly below the t-stat from a speaker that was installed when the previous owners had a security system. The wire looks to to be free for the most part the only issue might be fishing through the fire block, but I figure that was already notched out for this wire to be run.

The first picture is my furnace's logic board. The two conductor wire in the front is run to my AC Unit, the 5 conductor wire is obviously going to the t-stat (notice the blue wire just relaxing there), and the two conductor wire in the back is cut out side of the furnace. There is evidence of a whole house humidifier that was once installed (ties in to water pipe and a patch in the duct above the furnace) so it's possible that once went to switch on the humidifier when the furnace was running. Right?

In the second picture you can see where the 5 conductor wire meets the telephone wire again with the blue wire just hanging out. I'm thinking I can just connect the blue wire to the 'C' terminal and run new wire from this junction point to my t-stat. Am I thinking correctly?
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Last edited by mentalcase; 10-16-2012 at 05:25 PM.
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Old 10-16-2012, 06:02 PM   #11
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New thermostat with no 'C' wire


but beenthere it came from the internet IT HAS TO BE RIGHT......RIGHT.....yea right......ben sr
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Old 10-16-2012, 06:35 PM   #12
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New thermostat with no 'C' wire


Quote:
Originally Posted by mentalcase View Post
Alright. So things look easier then I thought. 5 conductor wire is actually run from my furnace and joins what looks like telephone (4 conductor) wire via wire nuts. Then it is run up to the t-stat. I have a big whole directly below the t-stat from a speaker that was installed when the previous owners had a security system. The wire looks to to be free for the most part the only issue might be fishing through the fire block, but I figure that was already notched out for this wire to be run.

The first picture is my furnace's logic board. The two conductor wire in the front is run to my AC Unit, the 5 conductor wire is obviously going to the t-stat (notice the blue wire just relaxing there), and the two conductor wire in the back is cut out side of the furnace. There is evidence of a whole house humidifier that was once installed (ties in to water pipe and a patch in the duct above the furnace) so it's possible that once went to switch on the humidifier when the furnace was running. Right?

In the second picture you can see where the 5 conductor wire meets the telephone wire again with the blue wire just hanging out. I'm thinking I can just connect the blue wire to the 'C' terminal and run new wire from this junction point to my t-stat. Am I thinking correctly?
The C on that terminal board is the common you need to connect to.
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Old 10-16-2012, 06:46 PM   #13
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New thermostat with no 'C' wire


You don't have to use common on your t stat you can still use that stat and run it off batteries you only need a common wire going to your condenser unit outside from the furnace board
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Old 10-16-2012, 07:01 PM   #14
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New thermostat with no 'C' wire


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You don't have to use common on your t stat you can still use that stat and run it off batteries you only need a common wire going to your condenser unit outside from the furnace board
Not if he wants to use he WIFI ability.
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Old 10-16-2012, 07:46 PM   #15
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New thermostat with no 'C' wire


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Originally Posted by bubsmaster25 View Post
You don't have to use common on your t stat you can still use that stat and run it off batteries you only need a common wire going to your condenser unit outside from the furnace board
Problem is, with the WiFi module installed in the 3m Filtrete, it will run the batteries down shortly within 24 hours.

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