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Furnace losing 24v when heat requested
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RP
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Furnace losing 24v when heat requested
wrote:
It's my understanding that there is no C on most wiring, because there
isn't a need for one.
Your understanding needs updating. In a typical resi HVAC system the 24v
secondary from the transformer has a hot and a common. The common isn't
necessarily grounded, but it is called common because it is fed directly
to one side of every load. In some systems the common is also switched,
but it is understood by any tech that common (C) is the transformer leg
that is not fed to R on the t-stat. HTH.
hvacrmedic
(Ungrounded light switches don't have a common
wire; they just connect the hot wire to the light.) All of the
appliances are grounded so you only need the power wire and a wire for
each device. Connecting R (24VAC) to a appliance's wire completes the
circuit and allows the appliance to run.
If it has worked for years then, yes, something has gone wrong. I
would verify the wiring and then call the furnace guy to fix the
problem.
Mike
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