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Boddhisattvha's avatar
Oct 19, 2013

Electrical Assistance with a furnace please

Hi all,
I just installed a new Suburban NT20 furnace and I need some help with the wiring. There's only four wires, red (hot) yellow(grnd) and two blue which are for the t-stat. My issue is that the damn installation manual makes no real differentiation between the two blue wires. There's a red and a white wire coming off the tstat and I assume red is hot and white is something else and they would need to attach to the corresponding blue wire(s). I don't imagine they are interchangeable? The wiring diagram only shows where the wires go in the actual furnace, but unless I take the furnace apart and track the wires I have no way of knowing which is which.

Anyway I got it installed and tried to turn it on and nothing happened. I switched the blue wires and still nothing happened.

I'm going to call Suburban on Monday but I figured I'd see if I can get it resolved with your help first.

20 Replies

  • Okay, I tried it and no go. I have a suspicion that I didn't get it grounded well enough. If that's not the case than either A. the furnace I just bought is bad or B. the hot lead coming in has issues. Are there any other possibilities I should look at?

    I actually just installed a new thermostat a few days before the old furnace died. (The old furnace just stopped lighting the blower motor was fine) The new thermostat is Heat only White Rodgers
  • What thermostat do you have? On a Coleman thermostat that operates the rooftop air conditioner, it does matter, as the thermostat gets its power from the furnace.
    Agree to try hooking the blue wires together first as a test though.
  • Yes, connecting the two blue wires should start the furnasce fan and then in about 10-15 seconds the heat should start.
    The thermostat is normaly just a contact closure.
  • You mean just bypass the thermostat and wire the blue wires to each other correct? And that should make the blower motor come on?
  • Hook the two blue wires together. If furnace dose not come on then you have other problems.

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