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My question is probably simple for those in the know. I've looked at the manual, and researched and Googled, however I'm still not confident. I tested this and got 24v on the red wire in bottom left when system was on heat and cool. I got nothing on the blue wires on the right. However, something just doesn't feel right. I'm trying to connect the C wire part on the Google Power Adapter. My system is a PGB030075-1.

So does anybody know which wire I need to connect the C on the Power adapter to?

1 Answer 1


The lower right (grounded) terminal is the C connection on the 24V side.

  • This is right but don't connect your C wire to the ground lug behind the transformer or to any of the terminals there. It's too close to the open live 120V wires, and any home-made connections you do with tape etc could end up touching those by accident. Follow those other two wires from that terminal to wherever they go, and look for somewhere convenient and safe to connect your C wire at the other end. Or cut one of them. Just keep your connection away from the 120V side.
    – jay613
    Feb 5 at 22:05
  • So I should connect to the yellow wire in this case?
    – AJ Rorie
    Feb 5 at 22:38
  • No, not the yellow. Follow one of the other two wires to where they connect, and add your C to that connection, or cut one of those wires and splice in your C connection.
    – Ryan.
    Feb 7 at 15:07

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