I'm installing an Ecobee 3 Lite thermostat. I needed to add the PEK at the HVAC control board. Here's the original wiring of the HVAC Control board. wiring at control board

As you can see, there are 2 wires at the Y spot. I installed one of the wires in the PEK, and left the other one as is.

Here's an image of the wiring after installing the PEK: wiring after adding PEK

Everything seemed to work well on the thermostat, but the AC is not blowing cold air. I suspect that it has to do with the wiring of the Y wire. Should I splice both of the original Y wires together, and insert that into the PEK? Or is something else wrong here?

  • + more points than I can give for taking a picture of the original wires before you started. So many people forget that!
    – JPhi1618
    Commented Oct 15, 2021 at 14:21

1 Answer 1


You should not need the Power Extender Kit for this install. The thermostat wire that has the green, white, red, and blue wire will also have a yellow wire in it. I think I even see the nub of cut yellow wire peeking out of the brown cable jacket. To simplify the installation, I would try and use that yellow wire.

Trim down the cable insulation on both ends and find the yellow wire. Then connect the yellow wire to the Y terminal on the air handler (along with the red that was there). Then connect the blue wire to the C terminal (along with the white wire that was there). Once that is done, then connecting the thermostat will just be matching colors to the correct letters: blue to C, yellow to Y, white to W, green to G, red to R.

If for some reason the yellow wire isn't usable because you can't access it on the thermostat side, you can make this work with the PEK. The red wire that was connected to the Y terminal needs to be put back under the Y screw. This is the signal cable that goes to your outside compressor. Right now the compressor isn't running because that red wire isn't where it is supposed to be.

  • Since the PEK is already installed, will it be as simple as putting the red wire back in the Y terminal and inserting the blue wire in the PEK? That would be the simplest solution, because I'm actually not on site, and have to tell my mother what to do ;)
    – Ben
    Commented Oct 15, 2021 at 14:32
  • 1
    @Ben, Ha, I understand that. Yes, the simplest way would be to put the red wire back under the Y terminal. I just wanted to have a complete answer showing the best fix.
    – JPhi1618
    Commented Oct 15, 2021 at 14:36

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