Puzzle about wiring to thermostat.

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Old 02-03-17, 05:57 PM
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Puzzle about wiring to thermostat.

I have a four wire bundle going from gas furnace to thermostat with only two connected. Red to RH and green to W. I just had a new furnace installed and the installer tried wiring the white wire from furnace to thermostat but furnace wouldn't run. I want to add a new thermostat that needs all four wires. I checked continuity of white wire and it checks out as being good but when I switch out the green wire and replace it with the white wire something kicks on in the furnace even though I have the thermostat set below the current temperature. A motor runs but the furnace doesn't come on and heat. What might be the problem here?

Thanks for any thoughts.

Peter.
 
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Old 02-03-17, 07:28 PM
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Welcome to the forums.

#1... Turn the power OFF while messing with the wiring so as not to burn anything up.

I'm a little concerned that your "installer" couldn't do what you wanted him to do.

The thermostat wiring connects to the furnace. The letters on the furnace need to match the letters on the thermostat.

You were using two wires before and now you need four.... why ?
 
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Old 02-04-17, 09:59 AM
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R, C, W and G.

It sounds like you may have a splice between the thermostat location and the furnace.

Is pulling new thermostat wire an option with your setup?

Battery operated thermostats might also be something to consider, but you would still need to identify the stat wires.

I have seen people get in a hurry to remove the old furnace and fail to write down the old control wire connections.
 
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Old 02-04-17, 10:52 AM
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I actually need five wires to install a wi-fi thermostat but was going to use the Venstar add-a-wire for the fifth wire. The installer hooked the thermostat up using the white wire but couldn't get the system to work so reverted to the green wire because it worked that way. The installer is a very good, highly rated, fourth generation furnace installer. The furnace is always switched off before making any changes.
 
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Old 02-04-17, 10:54 AM
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Ok... then right now....we're at the point where it appears the wiring is spliced somewhere.

Your only option may be to replace the cable.
 
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Old 02-05-17, 01:21 PM
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Pulling a new wire is not an option. It would be easy if my father-in-law hadn't added a ceiling in the basement thus covering up the wiring.
 
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Old 02-05-17, 05:39 PM
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If you can't replace the wiring then you need to assess what you have available.

Document the connections at both ends first.

You would need to disconnect both ends. Using an ohmmeter to check between all the wires. There should be no resistance/continuity shown between any two wires.

Short the wires at one end and check at the other end.
Short red and green..... check at other end.
Short to red and yellow..... check at other end.
Short red to black...... check at other end.
Etc.....
 
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Old 02-05-17, 05:42 PM
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What is the 5th wire for? stage 2 heat or stage 1 cooling?

The Redlink VisionPro TH8321R with a separate EIM will support up to 3 stages of heat and 2 stages of cooling with only 2 wires between the stat and EIM.

If you only need 1 stage of heat and cool the TH8110R is less expensive than the TH6321R.

You can add remote access with an internet gateway.
 
 

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