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Trying to install my new ecobee SmartThermostat. Furnace is a Trane heat pump, 20 years old from when the house was built.

When I looked at the existing thermostat, it has RGWY. Existing

So I thought I needed to install the PEK. I went up into the attic and found a wire nutted snarl. Someone probably assumed no one would ever have to look at their work ‍♂️

Anyway, it looks to me like the blue comes from the control box and is tied together with the white wire going to the thermostat, two white wires going back to the control box, and the wire running to the actual furnace.

furnace wiring

I added the labels. If I’m correct here, then what I actually have at the thermostat is GRCY. Does this make sense? Will this work if I use that white wire as C and have no W?

Oh, I also measured the voltage between R and W/C, and it read 28 VAC.

Thanks for the help

Update:

Here is the wiring diagram and control box wiring:

wiring diagram spliced bottom half top half control

Plus the heater wiring and diagram: heater

I pulled the rest of the wire out of the wall and the 4 wires tied back in the furnace are clipped off here, so I could theoretically do some rewriting if necessary.

Update 2: Unwrapping the tape

enter image description here enter image description here

It looks like they have the blue/C jumpered to the white/W using a capacitor.. Weird. I can’t think of any reason they would do that.. Maybe using it as a fuse? I’m so confused, lol

So I think I’m going to take the capacitor out, connect my thermostat C wire to the blue/C going to the AC, leave the white/W without the jumper. Thoughts? Should I leave it in?

Thanks again!

Steve W
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1 Answers1

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I ended up removing the resistor (or whatever), connected my blue wire from the thermostat to the C/blue bundle and left the white from the thermostat hooked into the white/W.

At the thermostat I hooked in the R, G, Y, C, and W. During initialization it didn’t detect the W, so I manually entered it. I tested both heat and cool, and everything worked fine.

The weird resistor jumper is still a mystery, but now that it’s working and installed, I’m happy to let it lie. Thanks for the suggestions and support!

Steve W
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