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I measured the voltage at the thermostat Rc to G and Rc to Y terminals, and they read 16.2V and 16.34V respectively. Shouldn't I be measuring 24V+/-? I purchased a Nest thermostat and it will not work properly at these unusual voltages.

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Is there a C wire at the thermostat? You should measure between R and C for a proper voltage reading.

Y connects back to the other side of the transformer through the coil of the contactor, in the condensing unit. G connects back to the other side of the transformer through the coil in the fan relay, in the air handler. C connects directly back to the other side of the transformer.

The only way to get an accurate measurement of the transformer voltage, is to measure between R and C.

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