Jumper to create a C wire ?


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Old 10-19-14, 06:38 AM
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Jumper to create a C wire ?

I have a TH8320WF that I cannot energize at the wall. I have an 8 wire run from the furnance, but only 4 (white, green, red, yellow) seem to have continuity from the furnance to the wall. I disconnected all the wires off the furnace and at the thermostat and checked continuity between all the wires. Only the four listed above are the only ones that showed continuity.

So ... I am lacking a c wire. Is there a way to jumper one of the other wires to get the constant 24v needed.

Running a new wire to the thermostat location would REALLY be a feat!
 
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Old 10-19-14, 06:59 AM
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Move the wire from G to C at the stat and furnace.

Place a jumper wire from Y to G at the furnace.

You must also verify that stat Y is connected to furnace Y if your jumper is going from furnace Y terminal to the furnace G terminal.

You should end up with 3 wires on Y, 2 wires on C,1 wire on W, and 1 wire on G if you have a single stage condenser installed on this system.

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Old 10-19-14, 07:40 AM
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I have an 8 wire run from the furnance, but only 4 (white, green, red, yellow) seem to have continuity from the furnance to the wall. I disconnected all the wires off the furnace and at the thermostat and checked continuity between all the wires. Only the four listed above are the only ones that showed continuity.
That is unusual to have 4 unused wires in the thermostat cable and not being able to utilize them. How did you check for continuity? One method is to (either at the furnace or the thermostat) select two of the unused wires and twist the bare ends together. Then go to the opposite end and test for continuity between those two wires. Set voltmeter to lowest ohms setting and touch leads together to see what the reading is. When you touch the meter leads between the two test wires you should get that same reading.
 
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Old 10-19-14, 10:20 AM
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Are you saying you have 8 conductors showing at each location but only continuity between 4? Have you checked to see if there are extra wires in the condenser that may have not been spliced through?
Just a thought.
Geo
 
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Old 10-19-14, 12:15 PM
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yes that is exactly how i did it. I show open for the unused 4 (orange, brown, black, blue) and for for the ones that worked with the old thermostat (that did not require a "c") red, yellow, white, green) I show continuity.

it is the stranget thing I have seen to have 8 wires at each end and to only have 4 that seem to run with continuity.....
 

Last edited by traveler11101; 10-19-14 at 12:27 PM. Reason: adding
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Old 10-19-14, 12:19 PM
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Yes 8 at each end. Not sure what you are asking on the condensor or how to check that. Could you eplain further?
 
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Old 10-19-14, 12:25 PM
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thanks for the diagram - very helpful. Having a heat pump with propane heat what functionality would I loose in jumping yellow and green togetner at the furnance?
 
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Old 10-19-14, 12:27 PM
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We're all trying to figure out how you checked the cable.

If you pulled the thermostat off the wall..... you'd only measure continuity between the four that were used since they are the only ones connected at the furnace end.

Did you try twisting the orange and brown together at one end and check for continuity at the other end ? If that does show open.... no continuity.... that leaves an unlocated splice in the cable.

========================================================

You can't utilize FAN ONLY at the thermostat. The fan will only come on when the furnace is up to heat or on a call for A/C.
 
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Old 10-19-14, 12:39 PM
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Thanks for reviewing this. Here is my testing method:

pulled thermostat off wall and disconnected all wires.
disconected all wires off of the furnance
- both ends have 8 wires (red, white, yellow, blue, black, green, brown, orange)

twisted the red and white together at thermostat and took ohm meter to furnance and measured continuity - good

then the red and yellow - good; then the red and yellow - good; then the red and black - bad; then the red and green - good; then the red and orange - bad; the the red and brown - bad. Lastly I measured the brown and orange - bad; and so forth all bad except for the 4 wires that were running my old thermostat (red, white, yellow, green).

How can I have 8 wires at both ends and 4 of them are not continuous???? Where would they be wired to and still end up at the other end?
 

Last edited by traveler11101; 10-19-14 at 01:22 PM.
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Old 10-19-14, 01:55 PM
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How can I have 8 wires at both ends and 4 of them are not continuous????
Possibly the installer used staples to secure the thermostat cable to the framing and accidentally hammered one side of the staple into the cable severing half of the conductors.
 
 

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