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    fish4brew's Avatar
    fish4brew Posts: 2, Reputation: 1
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    #1

    Oct 23, 2006, 05:10 PM
    Upgrade our 2 wire thermostat to digital?
    We have a thermostat that only has 2 wires, red and white coming out of the wall, and we want to change it to a digital thermostat with slots of W2, G, E, Y, C, B O, R or we also have a unit that has slots W1, G, Y, C, B, O, R

    So my question is this: Are we able to use either of the 2 new thermostats in place of the current ugly one we have?
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
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    #2

    Oct 23, 2006, 07:02 PM
    If you only have two wires it means you have heat only, no fan on/auto or cooling. Hook up the red wire to R or Rh and the white to W1. That's all you need to do.
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
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    #3

    Oct 23, 2006, 07:47 PM
    Read the directions. Some may require the common side of transformer to be connected to the C or B terminal. Many don't
    NorthernHeat's Avatar
    NorthernHeat Posts: 1,455, Reputation: 132
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    #4

    Oct 23, 2006, 07:50 PM
    Quote Originally Posted by labman
    Read the directions. Some may require the common side of transformer to be connected to the C or B terminal. Many don't
    Just C (common) Blue is for Rheem/Ruud/Weatherking heat pump reversing valve, Orange for about all other makes of heat pumps
    fish4brew's Avatar
    fish4brew Posts: 2, Reputation: 1
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    #5

    Oct 23, 2006, 10:49 PM
    Well, I hooked the red wire to the R terminal, and the white wire to the W1/W2 terminals on both units and no luck. However when I hooked the Red to R, and the White wire to C, OR the Red wire to B and again the White wire to C, it displays, BUT the heater doesn't turn on? The instructions don't tell how to hook up a two wire(red/white) thermostat. Anyone know where to put the red and white wires into the terminals? On another note, the instructions kept mentioning that multi stage thermostats shouldn't be used on single stage units... maybe this is the problem.. how do I know if I have a single versus multiple stage unit?
    labman's Avatar
    labman Posts: 10,580, Reputation: 551
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    #6

    Oct 24, 2006, 03:20 AM
    Chances are, if only had 2 wires originally, you have a single stage furnace. Look at it. If it just has a W terminal and no W1 or W2, it is a single stage furnace. Even if like mine, it could be wired as a 2 stage furnace, you will have to continue to run it as a single stage unless you run a cable with more wires.
    jeepiz's Avatar
    jeepiz Posts: 1, Reputation: 1
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    #7

    Oct 15, 2010, 05:32 PM
    NorthernHeat, you rule! I just struggled for about 2 hours wiring and re-wiring my new thermostat--didn't work until I read your simple R/Rh and W1 instruction above. The Honeywell directions and website were about as useful as a cookbook would've been. Thank you!!
    JD2883719's Avatar
    JD2883719 Posts: 1, Reputation: 1
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    #8

    Nov 21, 2010, 10:27 AM
    +1 for NorthernHeat - THANK YOU! Worked perfectly!
    Hannnydad's Avatar
    Hannnydad Posts: 1, Reputation: 1
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    #9

    Dec 11, 2010, 10:23 PM
    +2 for northernhear --- Got two thermostats in my house working. Thank you for the help :)
    douglasvb's Avatar
    douglasvb Posts: 1, Reputation: 1
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    #10

    Dec 25, 2010, 09:28 AM
    I also have a 2-wire setup. Do I need a battery powered thermostat? Because Rh and W1 don't seem to work for me on the new tstat.. screen is blank.. no lights.. R and W1 work on the old tstat, but its battery powered. Thanks!
    luke543210's Avatar
    luke543210 Posts: 1, Reputation: 1
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    #11

    Apr 28, 2011, 11:25 AM
    Hi there I need help with my room stat. it is very old with only 2 terminals red and yellow and I'm getting 12v down either red or yellow. I have a blue cable there as well but isn't connected. The new stat which has 4 terminals which are 2, 1, N, N. on the wiring diagram it shows to only use live in 1 and neutral in the first N but which cables do I use? *** help me?
    Seann's Avatar
    Seann Posts: 32, Reputation: 1
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    #12

    Apr 28, 2011, 10:04 PM

    In a 2 wire system u also need to check the voltage
    Mostly stats works between 20-30Vac or 750 milli volts but some stats might not work on 750 millivolts
    In 2 wire system we require battery power stats.
    jcoish's Avatar
    jcoish Posts: 1, Reputation: 1
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    #13

    Oct 23, 2011, 11:05 AM
    I have a gass furnass and neather of my two wires were color coded or marked so he told me the wire that goes to the murcury bulb goes to "r" and the wire that goes to the spring goes to "w". And if it does not work then just switch the wires. And the stat I hooked up was from the old simple style to the rth6400d stat. hope this helps anyone.
    melanie0128's Avatar
    melanie0128 Posts: 2, Reputation: 1
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    #14

    Nov 27, 2011, 02:03 PM
    NORTHERN HEAT ROCKS!! I have been looking for this answer ALL DAY!
    kyle9994's Avatar
    kyle9994 Posts: 9, Reputation: 0
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    #15

    Jan 12, 2012, 04:18 PM
    I hooked my 2 wire as follows: red to R and hooked white to G(its the fan switch). Make sure your fan switch on the thermostat is on AUTO. Adjust temp, Let it sit, it takes a few minutes to kick in, and presto. I have a old 2 wire heater/AC, u know the mobile home kind, that if I want AC I have to take cover off and flip the switch then put cover back on. Im using a T1040 battery powered stat. it works great!
    croye23's Avatar
    croye23 Posts: 1, Reputation: 1
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    #16

    Jan 29, 2012, 03:36 PM
    I want to replace a honeywell two wire thermostat to a hunter thermostat it has G RC RH Y/O W/B Y1.. the wires coming from the wall are red and white. I have heat and ac with the old one I put the new one on there and the heat will work but the ac will not can someone please help me out.. I'm about to loose my mind...
    Seann's Avatar
    Seann Posts: 32, Reputation: 1
    Junior Member
     
    #17

    Jan 30, 2012, 09:35 AM
    Hi
    None of the digital stat will work
    Need to get Honeywell CT30A.
    Because u have 2 wire heat and AC.
    ericsgold58's Avatar
    ericsgold58 Posts: 1, Reputation: 1
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    #18

    Apr 5, 2012, 11:07 AM
    Did exactly as you said and worked thank you very much
    atpalmer's Avatar
    atpalmer Posts: 1, Reputation: 1
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    #19

    Sep 17, 2012, 05:21 PM
    I have 2 black wires which were attached to an old mercury thermostat. I have a new Honeywell digital thermostat I would like it to connect to. How can I determine which letter code to connect them to?
    WestCoastRookie's Avatar
    WestCoastRookie Posts: 1, Reputation: 1
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    #20

    Nov 8, 2012, 08:40 PM
    NorthernHeat = #1

    Thanks for the help. Saved me a lot of time and curse words!!

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