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Anonymous asked in Home & GardenMaintenance & Repairs · 2 months ago

How to wire a smart thermostat? Dual Transformer system? R , Rc, W , Y , G. No C wire?

Is this system considered a Dual Transformer system? According to Nest since there is a R and RC cable it must be a dual transformer. But they were unsure and I don't know what that means! I don't have a C wire. Trying to figure out which smart thermostat is best suited for such a setup and hook it up without tearing up much or pulling new wires!

Hope the picture makes sense. I currently have a Honeywell Thermostat with the following wires hooked up.

R, RC, G, Y , W. No jumpers. I have a FirstCO Air Hnadler, Burnham Heat, and AC unit outside the house. Current Thermostat: Honeywell TH6220D1002 FirstCo Air Handler: 30MBX-3HW 120V-1PH-60HZ

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4 Answers

  • ?
    Lv 5
    1 month ago

    I'm geussing your old thermostat had a wire hooked to R an one to RC Doubt you have a dual transformer system.  Your A/C has a 24v control system.   Your gas furnaces problem runs on millivolt. Which is just the natural voltage on a closed circuit. 

    If you have a spare wire between the furnaces an thermostat you can use that as your common. You'll hook it to the common side of transformer. If I remember right nests have to have common theres no batteries.  But I could be wrong.

  • Anonymous
    2 months ago

    Return the thermostat.  Your system is not broken.  Do not fix it.

  • 2 months ago

    the manual for your hvac system has the hookup diagram you need for it and the Burnham manual the one for it  -- too bad you didn't give us model numbers

  • arther
    Lv 5
    2 months ago

    is your system using the jumper between r and rc? 

    Is it currently supplied by the system power or just a battery?

    would determine how to change it .

    with loop removed

    r is the power that comes for the heating unit transformer. switches to w when calling for heat

    rc is the power that comes from the cooling unit transformer. swithes to y when cooling call, y2 2nd compressor..

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