Question about Honeywell Programmable Thermostat Heater

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Hooking up new thermostat to new furnace

I have a honeywell rth7500d thermostat. i have the G Y W R hooked up and the thermostat is not on. i have a blue wire also not hooked up. it is not hooked up in the furnace either. should this be my 24 volt supply and where do i hook it up in the furnace?

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  • nwendtibc Jan 23, 2009

    what about "B" and "O"
    i hooked up the blue wire to c on the furnace and to b on the thermostat and the low volt fuse blew. the furnace instructions said to hook up c on furnace to b/c on thermostat for 24 volt. i am trying to power the thermostat so i don't have to change batteries and reprogram.

  • nwendtibc Jan 25, 2009

    What if a digital t-stat does not have a "c" terminal, but you want to keep it energized with 24 V? How is that done?



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Letter designations for honeywell tsats R=24 volt power, W=heat, Y=cooling, G=fan, C=common wire for the 24volt power to tstat. Generally R is the red tstat wire and so on. Blue tstat wire can be hooked up to common at the tstat. On the heater the blue tstat wire would be hooked up to the C terminal. But this also depends on the manufacturer of heating unit.

Posted on Jan 22, 2009

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  • HVAC TECH 2 Jan 24, 2009

    The O terminal is for heat pump reversing valve being energized in the cool mode and the B terminal is for reversing valve being energized in heat mode. If rev. valve energized from O tereminal for cooling and the coil were to fail it would failsafe to heat, and just the oppisite if B terminal energized and rev. valve coil would be failsafe to cool. Rheem & Rudd are tippically the only manufacturer that energizes the reversing valve off of the B terminal in a residential application.

  • HVAC TECH 2 Jan 24, 2009

    Follow up on the wiring, when you hooked the blue wire to the C terminal at the furnace you should hook it up to the C terminal at the tstat. The previous message I explained the O & B terminal. If you have a gas furnace you should hook up to C terminal. Also, did you get into the installer setup to set your thermostat up for your system. This thermostat is compatible for multiple systems. If this does not answer all your questions check out and on the home page on the right side of page 3 gray boxes, enter tstat # and click on the box to view installation guide to navigate through the installer setup. Hope all this helps!!!

  • HVAC TECH 2 Jan 26, 2009

    Everything that I see on the internet the top left should be the C terminal which is common to operate tstat without batteries. If your tstat does not have a C terminal then that may be a design change that has not been upgrades on the internet. Check out this web address Grey box labeled literature put tstat model # in and select above the model # highlight installation manual. If this does not help I will call honeywell on monday.



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