I'm looking to upgrade my old thermostat and need to run a c-wire. Where would be the best place to tap into?
Where to add a c-wire on the Goodman furnace
furnacethermostat-c-wire
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TR is Common on your unit, Every 24 volt device will have a Common leg as well as the 24 volt hot leg, just as a car battery has pos and neg, common is akin to neg in this case. Common is called this cause every 24 volt circuit terminates upon Common to complete the circuit. The last pic shown is the "time on" "temperature off" fan delay, the 2 lighter colored wires are low voltage, 1 id the heat circuits 24 volt hot leg being W or white, the other being Common or C. The gas valve has the same 2 24 volt leads as well, without completing the circuit nothing will work, every electric circuit requires 2 legs of power be it 1 hot leg and neutral/Common or 2 hot legs as in a 230 volt circuit. Google 40 VA HVAC transformer to see what they look like so you will be able to locate it. Your 2 wire thermostat will have only red and white shown on my diagram
Yes, you'll connect to any of the blue wires coming from the transformer.
If there's an empty terminal on the transformer, connect there. If not, you might be able to use a piggyback spade connector.
Otherwise, connecting at the point of grounding would be the next easiest location.
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Best Answer
Connect it to the junction of the fat blue wire and the skinny white wire
We know the fat blue wire in the foreground is a C wire, as it's currently returning current from the air conditioner compressor contactor (via chassis ground, which is odd, but it's what the wiring diagram on this unit calls out) already. The easiest place to splice into it is at the existing wirenut junction, although it appears you may have to hunt around for a spare wire in your existing cable if one is present but not visible, or pull a new thermostat cable if your existing one has no spare wires in it.