Help with installing new thermostat on old home (No C wire)

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Old 11-28-12, 12:12 PM
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Help with installing new thermostat on old home (No C wire)

[ATTACH=CONFIG]6129[/ATTACH][ATTACH=CONFIG]6130[/ATTACH]


Hi y'all,

I recently bought a house in St. Louis built around 1970 and never updated. We have been slowly renovating it and one of the last things I did was try to install a new thermostat with the winter coming soon.

The old thermostat did not have a C wire connected. The instruction manual that came with the Honeywell thermostat said that I could just run the thermostat off of the G wire. I inserted the G wire into the C spot and the heat and air conditioning work great...except, the fan is ALWAYS on.

Is there any way around this? As you can see there is a C wire coming off of the furnance and I also have a green wire unused upstairs at the thermostat.

Can any of you think of any solutions for me? I don't want to call in an electrician as I know I can do this with a little help!

Thanks in advance for your wisdom
 
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Last edited by Msarge16; 11-28-12 at 12:21 PM. Reason: Pics didnt work
  #2  
Old 11-28-12, 12:42 PM
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Help with installing new thermostat on old home (No C wire)

[ATTACH=CONFIG]6131[/ATTACH]
[ATTACH=CONFIG]6132[/ATTACH]

Hi y'all,

I recently bought a house in St. Louis built around 1970 and never updated. We have been slowly renovating it and one of the last things I did was try to install a new thermostat with the winter coming soon.

The old thermostat did not have a C wire connected. The instruction manual that came with the Honeywell thermostat said that I could just run the thermostat off of the G wire. I inserted the G wire into the C spot and the heat and air conditioning work great...except, the fan is ALWAYS on.

Is there any way around this? As you can see there is a C wire coming off of the furnance and I also have a green wire unused upstairs at the thermostat.

Can any of you think of any solutions for me? I don't want to call in an electrician as I know I can do this with a little help!

Thanks in advance for your wisdom
 
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  #3  
Old 11-28-12, 12:53 PM
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The green wire normally is for switching on the blower fan. By grounding it, that is what you are doing.

If the bottom of your picture shows the connections at the furnace, it would appear that the yellow wire is on the C terminal. Yellow is usually for air conditioning. If you do not have air, then use the yellow for the common at the T-stat.
 
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Old 11-28-12, 12:56 PM
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Go to the furnace and locate the circuit board or terminal strip.

Locate the G terminal there. If there is a wire from the thermostat connected to it, disconnect it and see if that causes the fan to quit running.

Record the color wire from the thermostat connected to each terminal on the strip--- R, W and so on, and report that here.

Generally speaking, energizing the G terminal causes the fan to run continuously. So you are checking to see if that is likely to be what is happening.
 
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Old 11-28-12, 06:47 PM
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Ok so I disconnected the G wire from the furnace and the heat ran but the blower did not. So that is clearly the fan wire. My problem I think is that I am using the G wire to also run the thermostat.

Can I rig this thing to be able to power the thermostat and also have the ability to turn the fan off?
 
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Old 11-28-12, 08:01 PM
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At the furnace, make a note of each terminal that has a wire to the thermostat connected to it.

Report that here, along with the model number of the Honeywell thermostat.
 
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Old 11-28-12, 08:58 PM
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What model is this new stat?

Do you have an unused wire at the furnace since you have an unused one at the t-stat?
 
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Old 11-28-12, 09:39 PM
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The stat is a rth6580

the bottom pic with the five wires attached is a pic of the wires connected at the furnace. The problem is that the wires colors don't match upstairs at the stat.

there is five attached at the furnace and four at the stat
 
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Old 11-28-12, 09:48 PM
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I'm reading that C,G,R,W and then what?


That wiring at the thermostat is really gnarly. Do you know where the new wire is spliced into the old wire?

A good practice would be to pull new wire from the furnace to the thermostat.

I still need the model of the thermostat as well.
 
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Old 11-29-12, 06:38 PM
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The stat is a rth6580
He gave it to you. It is a wifi stat and requires C.
 
 

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