My current wiring has 5 wires, R, Rc, Y, G, and W wires. No C wire. I've added an external 24V transformer and connected one wire to the C connector but don't know what to do with the other. If I connect it to Rc, then I have heat but no A/C or fan.

Any suggestions?

1 Answer 1


Don't use an external transformer. Find a way to run an extra wire from the furnace/air handler, and wire it as a proper C wire.

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