Can't Find The C wire Terminal in furnace for new thermostat

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Old 06-05-13, 06:51 PM
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Can't Find The C wire Terminal in furnace for new thermostat

So I just purchased a wifi thermostat that needs a C wire and I cannot get this to work.
This is how my old thermostat was wired up




and this is how my furnace is wired up. Bryant Plus 80t


I tried splitting the green wire so one would be in the "COM 24v" terminal and the other in the G terminal but that didn't work. then I tried both green wires together in the com terminal and it still hasn't powered on the thermostat.
Please help
 
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Old 06-05-13, 07:53 PM
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did you shut off the power before trying any of this? You may have blown the fuse on your control board. Somebody used phone wire instead of 18 awg solid wire for you low voltage to the thermostat... this may be causing an issue.
 
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Old 06-06-13, 03:36 AM
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I did shut the power off before switch the wires. I am going to go buy some thermostat wire today and run it down there. Just in case, how can I tell if I blew the fuse on the control board?
 
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Old 06-06-13, 03:46 AM
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Find the fuse and see if it is blown.
 
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Old 06-06-13, 04:00 PM
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If possible, pull a new 6+ 18 g conductor wire.

Also, you have a two stage furnace - to use it to it's potential, the w2 terminal has to be connected.

I'll post more info later if you're interested.
 
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Old 06-07-13, 10:19 AM
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Damn, Muggle I wish I read your post before I ran the 18/5 wire down there. But post about it, maybe I'll just run another 18g wire just for the w2. After running the new wire and then changing the fuse it all works perfectly now. Thanks a lot hvactechfw, i would have never seen that fuse.
 
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Old 06-07-13, 02:44 PM
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Two stage = 60-70% capacity on low, 100% on high.

Without a two stage thermostat, furnaces such as yours run on low for a few minutes at the beginning of each cycle, then switch to high until the t-stat is satisfied.

Now in colder weather, this causes the furnace to run on high when it's not really needed.

With w2 connected (and the furnace properly set up - ie there are dip switch settings that need to be changed), the furnace will only run on high when it's not keeping up on low; when high is no longer required, it'll drop back to low to maintain the temperature rather then quickly satisfy the t-stat and shut down.

The idea is to provide more consistent heat; odds are if your furnace is oversized (most are), it'll only run on high fire when you initially warm up the house.
 
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Old 06-07-13, 03:34 PM
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The idea is to provide more consistent heat; odds are if your furnace is oversized (most are), it'll only run on high fire when you initially warm up the house.
That's the way mine is. The ONLY time it goes to the second stage is if I manually push the thermostat more than three degrees about the current temperature. I have the smallest two-stage, variable speed furnace Lennox made at the time (70kBTU/hr.) and even in below freezing weather my furnace cycles on the first stage.
 
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Old 06-07-13, 08:57 PM
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^ Ideally it would start running continuously at 5-10F and use high fire fair bit in extreme cold. Many manufacturers don't seem to like making 2-stage furnaces in small sizes - kind of defeats the purpose.
 
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Old 06-08-13, 12:16 AM
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It might run continuously if it ever got that cold here. In twelve years the lowest temperature I have seen was maybe fifteen degrees F. and even that is unusually cold. Of course the time the power was out for three days and the inside temperature dropped to forty-seven it took several hours on the second stage to get it back to seventy degrees.

I have thought about changing the gas orifices and the induced draft blower's inlet orifice and downfiring the thing but I'm pretty sure that would cancel the warranty on the heat exchanger. Besides, I'm getting too old for such experimentation. Even in the milder weather it doesn't short cycle, on ten minutes off for twenty and repeating. I don't think it would have done that had the salesman gotten his way as he changed the order to the 90kBTU/hr model because it meant a bit less work in the duct transitions for the installation crew. Once I saw that I raised holy heck and demanded the smaller furnace.
 
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Old 06-10-13, 07:33 PM
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I have a little hiccup. My central air unit decide to turn on out of no where for 10 minute spurts when I have the thermostat off. Any answers to that?
 
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Old 06-10-13, 07:46 PM
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Which WiFi thermostat did you buy?
 
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Old 06-10-13, 07:50 PM
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Honeywell RTH6580WF wifi 7-day
 
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Old 06-10-13, 07:52 PM
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If it is all wired properly then it may be a bad stat.
 
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Old 06-10-13, 07:54 PM
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I'll re check the wiring tomorrow. Thanks again
 
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Old 06-25-13, 11:36 AM
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I noticed my AC wasnt working to well, So now I have this happening, freezing the pipes. I saw this and immediately cleaned the filter. Is that the reason why this would be happening?

 
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Old 06-25-13, 02:00 PM
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causes for ice to develop are poor air flow, or low refrigerant or a restriction in the refrigerant system.
 
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