DIY Home Improvement, Remodeling & Repair Forum > Appliances > HVAC > Carrier furnace fan won't switch on




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Old 04-08-2010, 09:20 AM  
Wuzzat?
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Originally Posted by Augment View Post
The blower motor was replaced a few months ago and the problems started then.
I think it's somewhat more likely that the problem is at the furnace end.


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Old 04-08-2010, 10:03 AM  
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I looked at the furnace,don't know where to start. Jumping the t-stat seems easier. What will this tell me if the fan does go on?



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Old 04-08-2010, 10:15 AM  
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I tried to jump on the tstat, nothing happened with green and red. I accidentally touched red and yellow, started fan briefly then stopped (a/c mode).

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Old 04-08-2010, 12:37 PM  
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What this tells us is that you could possibly have a bad wire from thermostat to furnace.
You'll have to jumper the R & G terminal at the furnace and see if the blower comes on.
Inside the furnace you'll see a wire coming in from the tstat.
Most likely brown insulation containing multiple colored wires.
What the thermostat does is completes a circuit of 24VAC from the R terminal to the G terminal to energize the fan circuit when fan "on".
If the G wire is bad, then power won't make it back to the furnace from the tstat. So now we must energize the G terminal at the furnace to eliminate this possibility. Inside the furnace you'll see the brown wire and it's multi-colored wires attach to the various terminals to run heat, A/C, fan, etc.
Touch the jumper wire to the R & G terminal and see if the fan comes on.

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Old 04-08-2010, 12:56 PM  
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I jumped the R & G terminals on the furnace and the fan did come on. I should mention the G and Blue wires seem to share a terminal, don't know if this means anything.

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Old 04-08-2010, 03:46 PM  
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On which terminal are the Green & Blue wires sharing (G or B)?

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Old 04-08-2010, 04:29 PM  
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G terminal

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Old 04-08-2010, 04:42 PM  
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That's curious, based on what your telling me the fan should work when switched to "On".
We are going to have to back it up a step as I can't readily affect a repair online.
I need to know what wires (color) are attached to what terminals on both the furnace and thermostat. Watch for crossed wires where the color and terminal does not match the opposite end (furance vs. tstat).
Just to be sure, this is not a heat pump system; correct?
We are definitely closing in on the problem but, I need more info to complete the picture.

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Old 04-08-2010, 05:19 PM  
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This is not a heat pump system, just forced air gas. I've noticed that the wires hooked up to the thermostat and then reappearing at the furnace don't match. On the thermostat there is an unattached blue wire, and attached white, yellow, green and red all attached to the correct terminals.

At the furnace, the thermostat wires are red attached to red, black attached to Y/Y2, white attached to W/W1, blue attached to green, orange attached to nothing.

I noticed that the green wire does not come from the tstat wires, it's in a separate bunch of wires of all colours. However, it's connected to the G terminal and there's another connection to the fan (a plug that you can pull in and out to different fan levels). Then the whole bunch leads back to the blower at the back of the furnace.

This is getting more and more complicated I think. Thanks for your help!

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Old 04-08-2010, 05:24 PM  
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Sorry, I forgot to ask whether there are any terminals where there are no wires attached on both the tstat and furnance ends.
Something is definitely mis-wired on purpose or on accident.
Not sure which is the case at this time.



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