Wires not color coded


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Old 12-15-22, 10:26 AM
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Unhappy Wires not color coded

Wires in thermostat are color coded so they match the wires coming from the gas furnace with A/C compressor outside. So I hurriedly disconnected them.
Wrong. Have two pairs of red and white wires coming out of the wall. Two separate cables with only the red and white wires coming out from each cable.
On the furnace or air handler end, the circuit board has one white wire connected to W1. The other white wire is connected to B.
One red and a yellow are connected to Y. The second red wire is connected to R.

Is there any way I can get the four wires connected to another thermostat correctly?

The first digital thermostat was installed in the 90's to a gas furnace. In 2004 got a new furnace and A/C. Now need to replace the digital thermostat.
Thought about just connecting one of the red and white and see if the furnace comes on. Though that may blow out the circuit board.
 
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Old 12-15-22, 03:16 PM
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HVAC wire color coding is not mandatory but when followed makes life easier. You need to identify each cable at the thermostat end so you know which white wire is W or B and which red wire is Y or R. Connect to t'stat accordingly. If the circuit board terminations are labeled per convention, W is heat, B is 24 vac common, Y is cool and R is 24 vac power. Don't know where the yellow wire comes from, but if the AC worked with the old t'stat, leave it there.
 
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Old 12-15-22, 08:34 PM
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That wiring sounds suboptimal and would probably be hard for us to decipher without pics at the furnace/air handler. If possible, I would run a new 18/8 wire which would be properly 'color-coded' and set you up for a smart thermostat one day.
 
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Old 12-15-22, 09:16 PM
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Welcome to the forums.

We could help you better if you described the situation better.
You should have connections on R, G, Y and W.
There should not be a B in your description.

Describe the cables separately. Doesn't matter yet which cable is which.
Cable 1 red wire =
Cable 1 white wire =

Cable 2 red wire =
Cable 2 white wire =

Fill in the four blanks and I'll tell you what to do.
 
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Old 12-17-22, 03:49 AM
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I just do not know which cable is which at the thermostat end. I wonder how the guys knew how to hook them up to thermostat. One of the cables must be from the original furnace.

Cable 1 red wire = R or Y
Cable 1 white wire = B or W1

Cable 2 red wire = Y or R
Cable 2 white wire = W1 or B

Also saw that the new thermostat has a red jumper from RH to RC. Should the jumper be left in place or removed?
Have picture but do not know password to download it to PC.

There is also a green wire attached to G but it does not go to the thermostat.

Thinking about getting a test light and connect a long wire from each terminal to the ends of the wires at the thermostat.
 

Last edited by TringTo...; 12-17-22 at 03:55 AM. Reason: Additionalinfo
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Old 12-17-22, 07:43 AM
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One trick you can do is disconnect the wires at both ends, then combine two wires and test for continuity with a multimeter at the other end.
 
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Old 12-17-22, 11:12 AM
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Ok..... you sort of answered the question.

You have two cables.....

Pick THIS cable at furnace and label 1.
red wire to R
white wire to B (common) C

This cable at the furnace will be 2.
red wire to Y
white wire to W1.

Mark the wires or cables so you can ID them in the future.
I use a Sharpie to put one ring on one cable and two rings on the second cable.
I would tape the white B/C wire black at both ends.

Temporarily take the white wire off of B at the furnace.
Go to thermostat end.
Pick either red (test) wire in one cable and touch to red wire on opposite cable. Does A/C come on ?
Now touch that same red wire to white of opposite cable. Does heat come on ?
If yes..... the cable with the red wire you used to test is cable 1.
If just the heat came on..... switch the cable and use that red as your test wire.
The red test wire that activates the heating and cooling is the R wire and is cable 1.

Cable 1 red = R (leave jumper connected)
Cable 1 white = C
Cable 2 red = Y
Cable 2 white = W





 
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Old 12-19-22, 05:45 PM
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Thanks for the info. This is a great help. Will try this out.

Tonight, used a test light. With switch at furnace off, connected red and white wires from one cable at the thermostat and used the light to see which terminals the cable was attached to on the furnace circuit board. Then reconnected them at the thermostat. Did the same with the second cable.
Thought it was working but temp did not rise. Then I stepped outside and could hear the compressor running. OH my.

Then I looked at the old thermostat. It had four terminal points red, white, blue, and green.

Thanks again for the help. Will try again.
 
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Old 12-19-22, 06:18 PM
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You may have the Y and W backwards. Y is heat and W is cooling.
 
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Old 12-20-22, 04:31 PM
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Still trying

And still cannot get photos off my iPhone or out of the iCloud.
Tried to follow directions but they do not coincide with the way wires are connected to furnace.
Today disconnected wires at furnace, one at a time, and used test light to ensure which wire is which. Turned on the HEAT and the A/C compressor came on. Switch thermostat to cool and compressor did not come on.


Cable 1
red wire to R
yellow to Y
white to W1
green to G

Cable 2
red to Y
white to B
 
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Old 12-20-22, 04:47 PM
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Old 12-20-22, 04:48 PM
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This is not what you told me. You said 2) two wire cables from the thermostat to the furnace.
That's red & white and red & white.
How did you get four colors on cable 1 ?

Cable two is the cable to the outside condenser. It is wired correctly.

OK..... your pictures are visible. You have a four wire cable at the furnace and 2) two wire cables at the thermostat. That means there is a splice somewhere.

If you have a meter..... with thermostat off the base and wires connected at the furnace....
At furnace... measure from R to the metal chassis. Do you get 24vac ?
If yes..... go up to thermostat and check all four wires to a known ground.
A known ground is screw on receptacle or switch plate.
Once you know R..... you can connect R to one other wire... one at a time to find the function.
 
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Old 12-24-22, 03:46 AM
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Thanks to your help now have heat.
Had to disconnect the white wire connected to B to prevent the A/C compressor from running.
 
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Old 12-30-22, 01:06 AM
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It is great to have the heat running again thanks to help from PJmax and others. So glad to not be running space heaters.
However, will need help to get the A/C running properly in April. I wonder if the thermostat is at fault.
 
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Old 12-30-22, 09:28 AM
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It would be most effective to run the proper thermostat cable and eliminate the splices and color duplications.
 
 

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