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  1. #1
    Join Date
    Feb 2011
    Posts
    17

    Easy Question about my Tstat

    Hello, I have a honeywell th8320 thermostat that is causing me to scratch my head. When i orginaly got this I installed it and its worked great since. well as I was re-reading the manual out of curiosity I found a setting in the installer options manual that allows for my back light to stay on dim with the 24v c connection. Problem is The manual says I need it connected to the 24vac C wire and from what I gather the c wire gets its power from the AC contactor 24v. Well I dont have AC so there is no power to my C wire for my backlight.

    Can I just jump it to the constant 24v R wire to get it to stay lit?
    I cant see it being a problem but i figured I would ask.

    rheem rgrm07meas
    honeywell th8320

  2. #2
    Join Date
    May 2011
    Location
    Ripley, WV
    Posts
    1,169
    You get 24 volts to the thermostat from the red wire on the "R" terminal which is tied to one of the taps on the secondary side of the transformer. The only way to complete the circuit necessary to operate the back light function like you described is to have a wire tied into the common side (opposite the red).

    Just as a side note if you try to DIY it, make sure the red and common do NOT touch because if there is no fuse in the low voltage circuit and they touch, it's bye bye transformer and big $$

  3. #3
    Join Date
    Feb 2011
    Posts
    17
    Well it was my fault.. I rechecked the setting in the T stat after fighting with it to get into service mode. (apparently theres 2 different service modes) I found the setting didnt save the first time i set it up. So i saved it and it lights up now.

    thanks!

  4. #4
    Join Date
    May 2011
    Location
    Ripley, WV
    Posts
    1,169
    No problem.

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