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Wiring honeywell digital stat

I have just brought a new honeywell digital thermostat T6620B1008(DT200) and i am having trouble wiring it up.
all i have on the new stat is A.B.C.conections

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  • Anonymous Dec 24, 2008

    yes same problem. not good diagram on diag e; what is "M" thanks jon

  • Anonymous Dec 24, 2008

    yea same prob diag 'e' what is 'M'

  • indpls42 Dec 25, 2008

    im having hard time connecting honeywell pro th 4000. old stat was a sc 2200 with emergency switch.. hw has no emergency heats but blower doesnt turn off and no cool air.. ty


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Hello davem1952,
The way you wire it will depend on how the other end of your three wires are wired into your heating system. This link
shows the various methods for wiring it and take into account the type of setup you are dealing with. You'll need to find the wiring detail ( last page) that corresponds to your setup..
Hope this helps..

Posted on Dec 13, 2008

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I tried to insatll my new honeywell programmable. the old t-stat had a white and red wire connected allread. there were 3 other wires unused, G,W,R. I hook up the original R,W wires to the new t-stat and...

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(normally wired with these colours)


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All you need to do is wire up the new stat with this in mind. (please note: if the wires are not colour coded like this then do not proceed and get an electrician)

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Go to
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it is always advisable to shut down the main swith to avoid further issues in replacing thermostat, if you follow the right color coding this should be no prob, unless otherwise it cannot detect the right temp then it will not stop until it reaches and senses the right temp.

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