I recently replaced my old American Standard thermostat with Google Nest. Cooling works fine but Heat does not work and simply goes into an unending loop of 'delayed: will start in 2:30 secs'

I think the problem is in wiring, and especially blue wire.
My wiring diagram enter image description here

Old Thermostat: enter image description here

New Nest Thermostat (If B wire in *OB, cool works and heat doesnt. If B wire is in C, nothing works) enter image description here

Board in the Attic: enter image description here

Also the wire connector test looks like this. Google search said the lin is way too high, but not sure what it means. enter image description here

Anyone has an idea what I am doing wrong? Thanks.

Update: updated the wiring diagram with a bigger picture. I bilieve i may have a heat pump outside the house. The outside installation looks like what google says is a heatpump. Also, zoomed out picture of furnace wiring: enter image description here

  • Is this a heat pump? Any idea what Iin and PS mean? Voltage should be 24v, so something is going on.
    – JPhi1618
    Commented Oct 18, 2021 at 20:42
  • I am not sure myself what those mean.
    – Gadam
    Commented Oct 18, 2021 at 22:52
  • @Gadam -- what make and model is your furnace? Commented Oct 19, 2021 at 1:30
  • @ThreePhaseEel I believe its American Standard Freedom 80 Comfort R. I just uploaded a zoomed out picture in the OP
    – Gadam
    Commented Oct 19, 2021 at 2:44
  • 1
    Also, the thermostat has to be properly set up for the type of system you have. You probably don't have a heat pump based on the wiring that I see. The only way to visually tell on the outside unit is looking through the fan grill on top and looking for a changeover valve, but then you need to know what that looks like. The thermostat wiring going to the outside unit is also different. A standard AC has two wires (like it appears you have), and a heat pump will have 3 or more.
    – JPhi1618
    Commented Oct 19, 2021 at 3:53

1 Answer 1


Your B wire is a C wire, so connect it to C at the thermostat

The wire you identified as B in your drawing is actually your C wire (we can tell because your A/C condensing unit is wired between Y and it, with only two wires headed off to it), so it needs to be connected to C on your Nest, not the */O/B terminal.

  • I came to to same conclusion, considering that I see the blue wire coming from the thermostat is connected to the B/C on the board. BUT if I connect the B to the C on Nest, it doesn't work. Both Heat and cool do not work. If I connect B to */O/B then Cool works but Heat does not work.
    – Gadam
    Commented Oct 20, 2021 at 3:37
  • @Gadam -- that's bizarre -- have you tried removing the jumper from Y to O on your control board? Commented Oct 20, 2021 at 3:52
  • No I haven't tried that. I can try. What is the reasoning behind it?
    – Gadam
    Commented Nov 5, 2021 at 17:25
  • @Gadam -- for a non-heat-pump system, there's really no reason for that jumper to be there -- a furnace control that didn't work correctly unless B was connected to something would be extremely astonishing to say the least, as it wouldn't work in the most common case Commented Nov 5, 2021 at 22:46
  • 1
    Yes, finally it works! The problem was in the Google Home setup. It asked me what wires do I have, and I selected RGYW and B, But when I switched to selecting RGYW and C because my Blue wire is actually a C wire. The fact that in the old thermostat (see pic above) the Blue wire was connected to B confused things a bit. Thanks @ThreePhaseEel
    – Gadam
    Commented Nov 14, 2021 at 4:19

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