My existing thermostat has 4 wires (missing C) so I'm attempting to use the Power Extender Kit (PEK) at the furnace control board. Only problem is, I only have 3 wires that are obviously labelled at the furnace (W, G, R). I have central air and I'd like to get my Ecobee3 setup if possible. Help. furnace[![][1]]2

  • Can you get us a wiring diagram for your furnace? – ThreePhaseEel Dec 28 '17 at 23:13

It is hard to see from the picture but if you look at the bottom 2 terminals on the transformer the one on the right is red and the one on the left is kind of blue/lavender. Red is typically “R” and the other one is typically the “C”. The top two wires are line voltage, don’t mess with those.

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