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Old 06-25-2009, 11:18 AM   #1
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Voltage drop at thermostat


I get 28v at the furnace controller at the R and C (red & blue wire) posts. At the thermostat i get 8v at the R & C (red & blue) wires. White,Green & Yellow are 28v. Is this normal or is this bad....Regards......Tom

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Old 06-25-2009, 02:01 PM   #2
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Voltage drop at thermostat


Is the common {C} terminal on the thermostat wired to the furnace. 28v between R and W,Y,and G is normal if the stat is not calling for heat or cool or fan.

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Old 06-25-2009, 02:48 PM   #3
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Voltage drop at thermostat


The common C wire (blue) is wired to the furnace controller but not wired to the thermostat. I've been told this common blue wire will need to be used if i upgrade my thermostat to a programmable lcd readout type thermostat. Is this a fact?.........Tom
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Old 06-25-2009, 05:44 PM   #4
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Voltage drop at thermostat


http://www.hvacmechanic.com/tstatwiring.htm

Post a schematic of 'stat to furnace wiring. We will find the missing 20vac.
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