C wire transformer


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Old 12-01-20, 01:23 PM
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C wire transformer

I have an A/C and heater and am planning to install a Honeywell smart thermostat. I donít have a c-wire on the thermostat side and the c-terminal on the furnace with the white wire seems to be used for the condenser.

I plan to use a Fyve 24 Volt Transformer, C Wire Adapter and plug it into the wall. Can I just wire the transformer wires into the Rc and C terminals and be set? I notice there is a metal plate on my current set-up which seems to connect R to Rc. Do I include this on the new thermostat?

My current thermostat and furnace set-up is shown below. Thanks!




 
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Old 12-01-20, 04:48 PM
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Which Honeywell are you going with? If it supports a K wire you can instead install an adapter and rearrange wires at the furnace to get a C wire. Note the K combines Y and G into one wire freeing up one for C.

http://cache-m2.smarthome.com/manuals/300673saver.pdf
 
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Old 12-01-20, 05:36 PM
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Ok- interesting. I am not savvy at all and have no experience doing this but Iím sure I can do a little rewiring of terminals at the furnace if that is best.
I am going with:

Honeywell Home RTH9585WF1004




I appreciate your help
 
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Old 12-01-20, 05:40 PM
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Welcome to the forums.

It is not a problem to put two wires on the C terminal. However you don't a spare in that four wire cable. Most reliable way is to replace the cable with more wires.

Astuff mentioned using the K wire. That works on four wires.
Posting the model number will help.

A separate 24v transformer would connect to Rc and C. No R jumper.
If your stat has the R slide terminal.... set it for two R connections.
 
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Old 12-01-20, 05:47 PM
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We posted at the same time. That thermostat has a K terminal which means you can use the Honeywell expander module. It requires slight re-wiring at the furnace end which is where that board goes.

Wiresaver module



 
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Old 12-01-20, 05:54 PM
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That thermostat shows that it supports a K wire. Get one of the modules below and some basic wiring.

Older model: https://www.amazon.com/Honeywell-THP.../dp/B0060ASWPE
New model: https://www.amazon.com/Honeywell-CWI.../dp/B07VMV2BJ7
 
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Old 12-04-20, 12:55 AM
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After weighing my options I decided to change the g-wire to the c-wire. I think it was the right decision given I didnít have to install any adapters and do much wiring work given Iím a novice.

I can live without using my fan independently. i only used it that way once in the last couple years. My smart thermostat is up and running- thank you for your help.
 
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Old 12-04-20, 02:59 PM
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That would mean you put a jumper from G to Y at the furnace board.
That will give you three wires on the Y terminal.
 
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Old 12-07-20, 08:16 AM
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Yes 3 wires on the Y terminal. It is working great and they fit fine. Is that ok??
 
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Old 12-07-20, 08:51 PM
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Yes sir....... that is ok.
 
 

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