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enter image description here[control module][1]We purchased a house last year and I am just now getting around to this. We are wanting to exchange our non programmable thermostat T6-NHP01-A to a programmable one (we have a nest). I have changed out thermostats before but never with wiring like this. The wiring from the furnace control board goes to a thermostat control module which converts it from multiple wires down to 2 wires. Can anyone explain what I can do to either remove the control module or how to wire the new thermostat? From the control board going to the Control module I have the following wires attached G,C,W/W1,Y/Y1,and R. From there it goes to the control module and connects to the same label of terminals. There is another set of 2 wires (Red and White) that plugs Red wire into Y/Y1 and White into Com. There is also a jumper wire between Rc/Rh. On the opposite terminal block there are 2 wires Red (V+) and Black(Vg) attached.

Thanks for the help.

Thermostat: thermostat wiring terminals

Control Module: control module terminal diagram

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  • That would depend on what kind of system do you have. We mortals have Cooling, Heating, Fan only. Do not have additional heater (gas, Oil, Electric). Do not have dual speed Heat Exchange fan (just single speed). That would determine how to wire it. So aside of 2 wires for 24 Volt, there are 3 wires for control. And maybe the C- (common) wire used for the electronics in the thermostat. Tell us what ou have.
    – Traveler
    Aug 9, 2022 at 20:30
  • Is replacing the wiring from the control module location to the thermostat control location an option? Also, can you post a photo of how the control module is actually wired, please? Aug 10, 2022 at 3:17
  • I uploaded the control module firing along with the wiring in the furnace control board. Yes I could run a new wire if I need to but would prefer not to if it’s not needed.
    – Thomas
    Aug 10, 2022 at 15:03

1 Answer 1

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Looks like the T6-NHP01-A is just the user interface module and the real brains are in the control module back at the air handler. The 2-wire connection back to the control module provides power and signal, but all the switching is being done back at the control module.

The Nest is a more traditional style in which all the switching is done at the unit itself and needs to be connected directly to the air handler control board via at least a 3 wire cable (more if you use cooling, heat pumps, etc.). You will remove the Honeywell control module from the wiring entirely.

Luckily for you, it looks like your builder already ran the multiwire cable already as the red and black wires from that cable are being used to connect the existing interface to the control module. All you need to do is make sure all the correct colored wires go directly to the air handler. You can splice inside the enclosure for the old Honeywell module if necessary - just make sure that module itself isn't part of the circuit anymore.

If you can provide a picture of the wiring terminals at the air handler and the existing control module, we can give more specific info as to how to wire it up. Without more info, we can only guess at which wires you'll need.

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  • The multiwire cable is behind the wall thermostat and runs down to the control module attached to the furnace (in the basement) but terminates there, can I just remove the wires from the control module and tie them to the wires that run up to the thermostat?
    – Thomas
    Aug 9, 2022 at 19:46
  • Yes, you should be able to do that. That's what I meant by splicing inside the Honeywell enclosure. If you have enough slack, you can also pull the wire directly inside the furnace.
    – Chris O
    Aug 9, 2022 at 19:47
  • Ok, so there is a Red and White wire that runs from the AC into the control module that get plugged into the Y/Y1 and Com terminals will those just be tied together as well with the other wires also in those terminals? Thank you for your help!
    – Thomas
    Aug 9, 2022 at 19:56
  • The extra Red/White wire is the signal to turn on the outside compressor. You're right - it needs to go to Y (red) and C (white) at the furnace control board. Red/white is used because it's cheaper than running a 5 or 7 wire cable to the exterior just so you can get yellow and blue.
    – Chris O
    Aug 9, 2022 at 20:01

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