Thermostat Install/ AC Wiring

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Old 05-27-20, 07:20 AM
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Thermostat Install/ AC Wiring

Hello,

I purchased a smart thermostat for my new house and ran into a few issues when I tried to install it. It looks like a previous owner/tech added the AC to the system by connecting it into the Thermostat wiring rather than running the wire the extra 2-ft required to connect directly to the control panel in the furnace.

My new thermostat Honeywell T5+ Wi-fi requires me to install a C-Wire adapter (which I can do no problem), however based on how the AC is hooked into the thermostat wiring I don't think the AC unit will work anymore once I add that in.

I'm looking for guidance on what to hook the AC up to on the control panel so I can simplify this process.

Based on how it is currently wired, I think the Red AC wire should go to "C" on the control panel, but really not sure where the white AC wire should be connected...

I'd love any thoughts.

Old thermostat (currently installed using the below wiring): Honeywell RTH230B

Here is a diagram showing how things are wired.

 
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Old 05-27-20, 01:08 PM
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Note: When I'm taking about AC I mean Air Conditioning.

(NOT Alternating Current) : )
 
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Old 05-27-20, 01:46 PM
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Which C wire adapter are you using? They're mostly the same but want to check.

To simplify things the white wire from the outside unit can go to the Y terminal on the furnace. Hook this up along with the black Y wire from the thermostat. Two wires are allowed under one screw for this type of wiring. Sometimes using the Y screw will cause the furnace to run at a different speed when a/c is called but deal with that if it happens.
 
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Old 05-27-20, 02:14 PM
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Thank you. I am using the Honeywell Home C Wire Adapter. Model: THP9045A1098.

So the White wire from the AC would go to the Y on the control panel, the Red wire from the AC would go to the C on the control panel and the Black wire from the thermostat would go to the Y on the control panel?
 
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Old 05-27-20, 02:49 PM
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Yes. What you said is correct.
 
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Old 05-27-20, 03:05 PM
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Do you agree there will likely be issues running the AC if I leave it wired as is, but add in the C-Wire Adapter between the control panel and 4 wires currently connecting to the control panel?
 
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Old 05-27-20, 03:30 PM
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You can't run it as it is..... you need that adapter to create a C to the thermostat.
Are you 100% sure there is not an extra wire in that cable.
It can be twisted around the jacket or cut off completely.
 
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Old 05-27-20, 03:52 PM
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Sorry if I wasn't clear. I will be adding in the C Wire Adapter. What I was wondering is if I need to wire the Air Conditioner directly to the control panel in order to make things work. I was concerned adding in the C Wire Adapter with the way the AC is currently hooked into the Thermostat wires would cause problems.

Yes. I checked there is no additional wire : (
 
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Old 05-27-20, 03:57 PM
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No..... the system will operate just as it was.

The Y screw terminal is usually just a blind connection point.
Some furnaces will run the blower faster if the Y terminal is connected.

Do you need a diagram for the C adapter ?


 
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Old 05-28-20, 05:10 AM
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Hi, how difficult would it be to pull a new cable ? C adapter is a MM fix , JMO
Geo
 
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Old 06-02-20, 03:42 PM
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Unfortunately, the previous owner finished part of the basement with a permanent ceiling, which is right below the thermostat, so running a new C wire would be difficult

I tried testing my old thermostat and switching the yellow wire to Y on the control panel and it didn't run very well. It would start and stop and start right away at the beginning every time it started up. Based on that I think I need to rewire so the AC goes directly to the control panel.

Here is a revised drawing showing the proposed wiring using the C-Wire Adapter and adjusting the wiring from the AC to run right to the control panel.


Does this look like it makes sense?

 
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Old 06-02-20, 04:06 PM
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Honeywell Lyric T5 thermostat.

Almost............. K from the adapter goes to K on the stat..... not Y as shown.
The R/Rc switch gets set up and then you use the one exposed R connection.
 
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Old 06-02-20, 04:56 PM
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I forgot to update the Thermostat in my diagram!!! Here is the corrected diagram. Does this look better?

Thank you all so much for the assistance!
 
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Old 06-02-20, 07:08 PM
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Looks like you're all set and ready to go.,
 
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