Upgrading Honeywell thermostats - Need help rewiring.

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Old 02-15-13, 02:42 PM
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Upgrading Honeywell thermostats - Need help rewiring.

I'm hoping someone here can help me out. I've never so much as touched a furnace (electrically speaking) so this is all new to me. I just bought a Honeywell RTH8580WF WiFi programmable thermostat. I am replacing a Honeywell RTH6300B thermostat. The furnace is a Carrier Infinity 80 gas furnace and there is also central AC.

Sure enough, I don't have that elusive C wire at the thermostat. But, what I do have is a set of wires which seem to both originate at the "R" terminal on the furnace and bot end up at the "R/Rc" terminal at the thermostat. These wires are red and orange. All wires are labelled at the thermostat end except for that orange wire.

What I've read tells me that the "C" wire is a 24V common. I did locate a terminal labelled "24V COM" on the furnace and it currently has a heavy black wire and a white wire (not the same white wire which ends up at the thermostat). What Id' like to know is, can I take that orange wire from the R terminal at the furnace end and move it to the 24V COM terminal and at the thermostat end use the orange wire in the "C" connector?

I don't see the benefit of 2 wires going from and to the same place but I'm also not an electrician or knowledgable in the area of furnaces, so maybe there is a purpose to this.

Images attached. Sorry for the less than great pics but it's hard to get in there and the wiring is not the cleanest. I didn't want to touch anything so I did the best I could. In image 1, the "COM 24V" terminal is the 5th one and the "R" terminal is the 8th one.

If you have ideas as to how to do this better, I'd welcome them.

Thanks.





 
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Old 02-15-13, 04:38 PM
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yes, use the orange wire as C at the thermostat and connect it to the 24V common terminal in the furnace along with the other wires. DO NOT remove any of the other wires on the furnace terminal as they are there for a reason.
 
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Old 02-15-13, 04:49 PM
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Will do, thanks. Appreciate the quick response.
 
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Old 02-15-13, 06:48 PM
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Do you have any other wires?? I see W2 isn't wired up, so you are not taking a full advantage of a true two stage on your furnace..

If you don't are you able to run a new wire up there??
 
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Old 02-15-13, 07:10 PM
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There are no unused wires, with the exception of the orange one which isn't so much unused as it is unnecessary in its current role. Now, some clarification is needed. You said I'm not getting the full advantage of the furnace. If the W2 was wired up, what would it do? Yes, I am very new to this.

Right now the furnace runs on what I call the "low" fan setting most of the time, kicking up to the high fan setting (really loud) rarely and only when it needs to (my guess is it does this if it fails to get to the thermostat preset temp in some period of time). I always thought this was the second stage. Is it?

Currently it's not easy to get a wire from the furnace to the main floor as the cable goes alongside the ductwork then disappears upward (this is likely at the point directly below the thermostat). It's hard to see where it's actually running but I'm sure if I really wanted to I could fish a new wire up there. However, it seems a little ambitious given the critical role the furnace plays and my minimal knowledge of it.
 
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Old 02-15-13, 07:36 PM
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Right now, your furnace is "timed" to go into 2nd(high) stage. So if you had a long run time, after 10 or so minutes of run time, it will go up into 2nd stage as you mention.

Where if you wired up W2, it will run 1st(Low) stage pretty much the whole time.. Only time 2nd stage will kick in if 1st stage can't keep up on the coldest day, and when the stat comes out of set back/recovery mode.

If you can't run new wire, then just have to leave it be.

Also, go into the advance setting, and set the system type/CPH to 3 for best results.
 
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Old 02-17-13, 11:34 AM
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Done! Thank you both for your help. Everything is working correctly. Love this Honeywell WiFi thermostat. The installation went smoothly and everything works as advertised.
 
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