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I have a Lennox G14Q3 propane furnace (forced air). I used the Nest/furnace setup last winter without any problems with just the W and R terminals. But, these summer days I would like to push air through the house with the blower (without heat) and remove it with my HRV system.

I’ve tried hooking up the terminal G to the G terminal on the Nest (for the fan). But the Nest can’t seem to turn it on.

Note: When I test the heat with the Nest, my furnace goes through it’s standard cycle of heating up then turning on the blower.

Also, I can’t seem to get the blower going down at the furnace by shorting R and G, shouldn’t that work?

Thanks, Josh

Edit, added model and diagram pictures: enter image description here

enter image description here

EDIT 2: I realized that ACC isn't actually connected to anything. It gets 120VAC when I switch the relay, but there is still no path to the blower to be energized. Could I just take one of the speed wires from the blower motor and connect it to ACC so that it acts as an indoor blower? enter image description here

  • Do you get 120V from ACC to N when you jumper G to R on the furnace? – ThreePhaseEel Sep 24 '17 at 13:25
  • Did you re-do the initialization cycle with the Nest where it discovers what kind of heater it's attached to, and what features it has? – Harper Sep 24 '17 at 13:25
  • @ThreePhaseEel I get the standard 24VAC between G and R, until of course when I short them. – Josh Jobin Sep 24 '17 at 13:39
  • @Harper yes, the Nest detected the W, R and G lines. C isn’t connected, but when I did connect it, the Nest didn’t boot. I’ve read that’s because it detects incorrect wiring – Josh Jobin Sep 24 '17 at 13:40
  • @JoshJobin -- can you measure the voltage from ACC to N while G and R are shorted together? – ThreePhaseEel Sep 24 '17 at 13:40
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Alright, I figured out why it wasn't working. Had nothing to do with ACC not having a lead. I was looking at my setup closely and noticed that only 2 wires were coming up from the motor, but it needs 3. I noticed that there was a wire coming from pin 3, but it was crimped and didn't run to the motor. So I looked at the speed table and decided I wanted to run the Brown wire up. Connected it to pin 3. Now when I short R and G, the fan turns on :) enter image description here

  • That'd do it :) BTW: you probably should replace this furnace soon -- there's no telling if the previous owners did anything re: the recall, and HX leaks in furnaces are something that's way better to be safe than sorry about. At a bare minimum, I'd have the HX pressure tested ASAP as per Lennox's instructions on the matter. – ThreePhaseEel Sep 27 '17 at 22:14

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