I have another post with this question (Adding a C wire) but thought I'd clear up any confusion with this new post and I'm adding a diagram also. The diagram shows my current thermostat wiring and not the new Ecobee one.

I cannot add a new thermostat wire, which would be the best way, so I'm going to go with the Ecobee's PEK module. Just wondering where in the line I should add it.

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The manual says to add the PEK at the control board on the air handler but I have some wire nuts along the way that connect other things. So my options are:

  1. Connect the PEK at the control board but then the EZ trap and condensate pump will go through the PEK wiring module at R. Also, the Y wire will have the AC white wire connected to the PEK.

  2. Connect the PEK where the wire nuts are but I will have to connect the C wire from the PEK to the blue C wire, white Humidifier wire and red AC wire. Is that ok to do?

I'm thinking 2 is the better location for the PEK but let me know your thoughts. Also, if I were to use a 24 volt transformer, could I just connect C at the thermostat to one of the screws on the transformer? Or would I have to connect the other screw to something?

Thanks for any help.

1 Answer 1


Alright -- the trick with the PEK for you is to treat everything wirenutted to your two thermostat cables as the "furnace" from the PEK's standpoint. You'll need some 18AWG pigtails for the connection from the PEK to the "furnace", though, as follows:

  • Red/black nut to PEK cover (furnace) R
  • White nut to PEK cover (furnace) W
  • Green nut to PEK cover (furnace) G
  • Yellow/white nut to PEK cover (furnace) Y
  • Blue/red/white nut to PEK cover (furnace) C

and then you can connect the base as follows:

  • Red Left to PEK base (t-stat) R
  • White Left to PEK base (t-stat) W
  • Red Right to PEK base (t-stat) G
  • White Right to PEK base (t-stat) Y

Just make sure to connect the Red Left (R) wire at the thermostat end to the Ecobee's Rc terminal or else the Ecobee won't turn on (this is a limitation of using the Ecobee/PEK combo).

  • Thanks again ThreePhase. That's the way I was thinking of wiring the PEK but just wanted to make sure all those other components would be ok to connect with the PEK and that I was doing it right. Thanks for clearing it up.
    – robk27
    Jul 18, 2016 at 21:48

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