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It sounds like you are talking about the multiple taps on the heater control transformer (blue wire, black wire, etc). These transformers have a primary (high voltage side) and and secondary (low voltage side). Arbitrarily hooking up the thermostat common to random wires such as the unused blue wire is not a good idea because unused wires are definitely ...


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Check your set points. You'll want to have a degree or two between the heating and cooling set points. For example, if your cooling set point is 76°F, you'll want to keep the heating set point at or below ~74°F. Check the documentation for your unit, to determine the recommended buffer value. Also note that some units allow you to program the ...


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The red wire that is currently on the C terminal, runs out to the coil on the contactor in your condensing unit (A/C). You'll notice the white wire from the same cable is on the Y terminal, which connects to the other coil terminal on the contactor. Technically you shouldn't put two wires under a single screw terminal, but it's done quite a bit with HVAC ...


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I encountered a similar issue, except that the root cause may have been the 3M radio stat (wifi enabled) thermostat ran out of batteries... which it uses instead of the input voltage (R) to control the thermostat. The manual says never let it run out of batteries (which seems impossible... bad design). In tracing the issue, I found a light on my furnace/air ...


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If I had to guess I would say that the red/white pair go off to a separate (maybe replacement) transformer was added. Kind of like the transformer you often see sitting around in an attic or crawlspace that powers a doorbell. If you meter across those two wires, I'm guessing you will find around 24 volts AC. Such a transformer is usually built into the ...


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This is my attempt to "demystify" the whole "C" wire thing for non-technical folks. This explanation intentionally ignores lots of details that are not relevant to a basic understanding of the concept. An old-timey thermostat is mechanical in nature. You can think of it very much like 3 separate mechanical on/off switches. (the "switches" in this case are ...



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