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I need help connecting a new 'C' wire for a Honeywell RTH6500WF thermostat.

Current Wiring Diagram As you can see the heating is an old boilder with a simple pump to circulate the hot water to the baseboard radiators.

The A/C has 3 connectors to it. A/C Schematic

This is the circuit board in the Blower AC connectors

This is the current thermostat current thermostat

I know I need to run a new wire for the additional wire but WHERE do I terminate the 'C' wire to on the thermostat? on the C terminal inside the A/C blower?

That wire runs to the compressor outside and then to the Y terminal of my current thermostat. Do I just need a new transformer? and how would I create the circuit on that.

Any help would be greatly appreciated.

Thank you.

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    I’m voting to close this question because it's abandoned – FreeMan Dec 11 '20 at 13:10
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You want the C terminal in the air handler, yes

The terminal you're looking for is indeed the air handler's C terminal -- it's on the fan-delay board (in the back left, from the viewpoint of the picture you've posted). You'll want to tap the connection it's making to the blue wire using a "piggyback" tab terminal or by cutting and splicing into the blue wire connected to it with a wirenut.

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