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    hensoc3's Avatar
    hensoc3 Posts: 2, Reputation: 1
    New Member
    		  
    #1

    Dec 2, 2009, 11:58 AM
    Thermostat wiring question
    I have an old white rodgers mercury switch 4 wire thermostat for a heating/cooling system that has terminals marked as w, y, g, and rc with rc jumped to a terminal marked 4. The new Honeywell ct31a thermostat has terminals marked w, y, g, and r. It says to conncect y to y, w to w, g to g, and connect r to rh r or 4 and if you have a terminal marked rc that you cannot use this product. Can I still connect to the r terminal even though I have an rc terminal? I also bought a LUX t10-1143sa thermostat and its wiring shows attaching my rc to its rh which is then jumped to its rc. So can I just do that with the honeywell as well. Which new thermostat should I use and how do I attach. Thanks.
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #2

    Dec 2, 2009, 02:30 PM
    What is the exact part number of the old thermostat?
    hensoc3's Avatar
    hensoc3 Posts: 2, Reputation: 1
    New Member
    		  
    #3

    Dec 2, 2009, 03:25 PM
    The only number I find on it is stamped on the inside cover as 1072C. The terminals are marked y, w, g, and Rc but the Rc is jumped to a terminal marked 4 which I assume are the heat and cool power. The new thermostat has only w, y, g, and r.
    KC13's Avatar
    KC13 Posts: 2,556, Reputation: 99
    Ultra Member
    		  
    #4

    Dec 2, 2009, 05:09 PM
    The "Rc" & "Rh" terminals are provided on some thermostats if the system has separate control transformers at the indoor & outdoor units. When a single transformer is used, these terminals are "jumpered" together to provide power to both. If you only have one "R" wire coming from the wall, either transformer will be suitable.
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