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Old 12-01-2015, 11:44 AM   #1
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Furnace Fan won't come on

Hi Folks, I'm trying to figure out where the 12V power to my furnace is routed. I have jumpered the fan itself and it works. Brand new Dinosaur board is installed. No blown fuses that I can find. The 12V terminal marked "furnace" on the panel is not wired. The thermostat signal to the furnace is through the a/c. When I switch the thermostat to "heat" I can hear a relay in the a/c click but nothing at the furnace. Furnace fan will not come on at all. The power wires at the furnace are a molded pair red white/white and I have not been able to find where it is routed from.
Is there another fuse hidden somewhere? Any other suggestions?

Thank You,
StephenD
2006 Work/Play 28'
Furnace is Suburban NT20S
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Old 12-01-2015, 01:25 PM   #2
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Did you check all the fuses in the panel to see if any of them are blown?

There may be a fuse in the A/C control box that goes to the furnace.
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Old 12-01-2015, 01:39 PM   #3
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Yes I did. I've come across misslabled panels before. There is a 5amp fuse in the ac board that is good.
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Old 12-01-2015, 04:44 PM   #4
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I restored power to the furnace (bad ground). Now if I pull the two wires labled "to furnace" that are located at the ceiling ac and jump them together my furnace will run but without t-stat control.
So my problem is either the t-stat or the board located in the ac. Can anyone tell me how to know for sure which one is the problem?
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Old 12-02-2015, 01:26 PM   #5
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Quote:
Originally Posted by StephenD View Post
I restored power to the furnace (bad ground). Now if I pull the two wires labled "to furnace" that are located at the ceiling ac and jump them together my furnace will run but without t-stat control.
So my problem is either the t-stat or the board located in the ac. Can anyone tell me how to know for sure which one is the problem?
Maybe there's someone who can give you a technical answer to your question, but here is one that is not. If it was me, I would replace the least expensive of the two first. If it's the thermostat and you've wished to install a better one than you have, now would be the time to do it. After replacing the thermostat and if the problem still exists, then try a new board. Good luck, but make sure all the electrical connections are secure and there are no blown fuses before you begin spending your money.
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Old 12-02-2015, 02:07 PM   #6
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Quote:
Originally Posted by StephenD View Post
Hi Folks, I'm trying to figure out where the 12V power to my furnace is routed. I have jumpered the fan itself and it works. Brand new Dinosaur board is installed. No blown fuses that I can find. The 12V terminal marked "furnace" on the panel is not wired. The thermostat signal to the furnace is through the a/c. When I switch the thermostat to "heat" I can hear a relay in the a/c click but nothing at the furnace. Furnace fan will not come on at all. The power wires at the furnace are a molded pair red white/white and I have not been able to find where it is routed from.
Is there another fuse hidden somewhere? Any other suggestions?

Thank You,
StephenD
2006 Work/Play 28'
Furnace is Suburban NT20S
With the T stat in the heating mode you should have 12 volts on the white wire leaving the T stat If you don't its t stat or if it is an electronic stat it may not be switch over to heating mode. If you do then the problem is with the control board in the ac unit or the wire to control board.

Hope this helps Tim
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Old 12-02-2015, 03:48 PM   #7
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We have a 2015 Sabre 5th Wheel. Furnace comes on, but when it first comes on it SCREAMS this 2 second noise - runs normal - then turns off with the same noise. We had it to the Dealer, they fixed it, ran good when we were there. But the first time using it ourselves, it's doing it again. DH thought it was some sort of belt - Dealer said "design" - I bet that's the classic answer. We don't use it that much because we have the fireplace and WE LOVE THAT When we wake up in the morning and just want to take the initial chill off, we turn on the furnace - but then it's on with the fireplace. It gets so hot during the night I usually get up and turn it off!! It's funny, that's the one thing we didn't want, we got it anyway and now we wouldn't trade it for anything
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Old 12-02-2015, 04:10 PM   #8
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According to the following wiring diagram, I'd jump out the two thermostat wires inside the T-stat and see if it'll run. If it does then the problem is in the T-stat.

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Old 12-02-2015, 04:15 PM   #9
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I had much the same noise when I turned on my heater. Dealer said same thing bad design. But one night I turned it on and the noise went to a sound of parts breaking apart. After exam I found that a fan relay inside the fan casing came loose and went into the moving fan blades ripping them all off. Bought a new van blade and installed and tightened down the relay and for added security I also put some high temp silicone to insure it would not happen again. I agree it is a poor design having this relay installed with just 2 small screws less than 1/8 of an inch from the blades but the dealer still should be able to make a permanent fix much like mine.
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Old 12-02-2015, 07:40 PM   #10
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Thanks folks, TimVWulp had the advice that worked. The problem is in the board. Of course that board and t-stat are "obsolete" and for $100+ I can get the "updated" t-stat / relay board package. My neighbor suggested I install a separate t-stat for the furnace. I can get t-stat for a lot less than the new parts. So now the question is: Is there any reason I shouldn't run my furnace and ac with separate t-stats?
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