Plumbing, Electrical, & HVAC

Honeywell Thermostat Wiring Instructions

When in the market for a new Honeywell thermostat, make sure you understand your Honeywell thermostat wiring needs before upgrading.

Q: I installed my new programmable thermostat, but it won’t turn on.

A: If you plan to upgrade to a new thermostat make sure you have the proper number of wires available, otherwise your new thermostat won’t work. If you do need additional wires, you will want to consider how difficult installing new wires will be for your application, and if you need to budget for an electrician or hvac tech to install the proper wiring.

Modern electronic thermostats are no different from any other technology, in that they can do more, but can also seem complicated to install and understand. One comfort to know is the basic wiring hasn’t changed much, with exception of an additional wire to get some programmable digital thermostats operating.

Note: For specific thermostat model installation manuals and wiring instructions, refer to our Thermostat Buying Guide for a complete list and link of manufacturers. Individual thermostat model information is most likely the best place to find particular manuals, and not a general manuals category that can be found within the search function.

SEE ALSO: In-Depth Thermostat Wiring Explained
SEE ALSO: Heat Pump Thermostat Wiring
SEE ALSO: Manufacturer Thermostat Installation Manuals – manuals online or manualslib

4 Wire Honeywell Thermostat Wiring

  • G – Fan (green wire)
  • R – 24 VAC / Rc and R or Rh (red wire)
  • Y – Compressor / air conditioner (yellow wire)
  • W – Heat (white wire)

Note: A previous installer may have used a different set of color wires. This will be a non issue to keep track of if a whole new set of thermostat wires is pulled. Otherwise tag the wires before removing from the existing thermostat, or take note of the terminals each wire is attached to.

honeywell_CT87N

 

5 Wire Honeywell Thermostat Wiring

Some programmable thermostats (e.g. Honeywell Prestige wiring requirements) need a minimum of 5 wires, and maybe more depending on what features you want to operate (humidifier, etc). The additional 5th wire will be for common (neutral), which acts the same as it does on an electrical light switch to complete a path and provide power for the display, closing switching relays, etc.

  • G – Fan (green wire)
  • R – 24 VAC / R and Rc (red wire)
  • C – 24 VAC Common (color can vary per manufacturer – may be blue, purple, brown. etc.)
  • Y – Compressor / air conditioner (yellow wire)
  • W – Heat (white wire)

honeywell_thermostat

 

Furnace Electrical Board Connections

Going into your furnace may sound intimidating, but if you have the basic knowledge of wiring, and know how to remove the proper furnace panels to access the electronics, then you should be fine. The COM 24V terminal will be connected to the C (24 VAC common) of the thermostat.
furnace_terminals

 

How to Install Thermostat Wire

If you have easy access to the existing thermostat wires, just remove and follow the same path with the new set of wires. You can use cable ties, electrical tape, or staples (securing wires and cables article). Be sure to take a very conservative measurement on how long your new set of wires should be. You don’t want to start over, if you come up short.

Any home improvement store should carry thermostat wiring. Also check local electrical and lighting supply houses.

If wires pass through a floor and up into a wall cavity before reaching a thermostat. Try the following.

  • Start at the thermostat location. (i) A simple trick for pulling new wires to replace existing ones: tape one end of the new wires to the end of the existing wires coming through the electrical box or wall opening. Make sure to tape completely over the wire ends, so no edges are present that can snag something. (image below)
  • Slowly pull the new set of the wires down through the wall from the basement. (i) Use any object larger than the hole in the wall, and tie or fasten to the end of your new wires, so you don’t pull all the wire through the wall. e.g. pencil or flat washer, to act as a stop. Use electrical tape to secure if necessary.

taped_wires
In a situation where the original thermostat wires may have been stapled to an interior wall stud, and not run through conduit, you may be better off leaving the existing set of wires, and cutting them off at the entry and exit points of the wall. Then feed new wires with a fish tape (Klein Tools). Check your local home improvement stores, or local tool rental, for rental availability.

CAUTION: ELECTRICAL HAZARD – Always turn power off before performing any work. Contact a certified HVAC tech if you don’t feel 100% sure of your DIY capabilities.

 

69 Comments

  1. 1

    I’m replacing a White-Rodgers thermostat with Honeywell RTH7500D. My AC wiring consists of G, W, RC, RH (a piece of removable wire that was connected to the RH and the RC), and 2 Yellow wires that were connected on the same terminal. Question 1: Where should I connect the yellow wires? Question 2: What do I do with the piece of RH wire? Thanks for your assistance.

    • 2

      Update: I only had 1 Yellow wire. The other yellow wire was connected to the old thermostat. I was able to connect the new thermostat and it is running nicely. However, my lights are flickering. Question: What is the RH wire for, and do I need to connect it? Thanks again.

      • 3
        • 4
          • 5

            Hi Chris. I did call Honeywell and they helped me to program my AC. Did you program it? Now, mine is still not cooling so I had to call my AC tech. I wish you well.

          • 6

            Chris, the tech just left. He said that the AC capacitor had gone out. I asked him what is the capacitor. He said that it turns the compressor on. That’s why my lights were flickering because it was trying to kickstart it but it wouldn’t budge. So try that. I hope it helps. He did tell me that I did a good job installing my own thermostat because it’s a tricky one. I praise God that it all worked out. It’s cooling nicely now!! He charged me $200. Be blessed.

          • 7

            This is a great example of how not everything can be solved on the internet. Many issues need a hands on approach by an experiences technician. Glad you’re up and running smoothly now Tracie. We appreciate your responses and willingness to help others that may come across similar problems.

          • 8

            Denny, you’re welcome. Thank you!! Yes. You are correct about seeking an experienced technician. However, many times we seek the internet as a means to save money and not to be forced to call someone for everything. As being single, that’s why I attempt to do things myself, because I will never have any money if I have to constantly call someone for everything that happens in my home. Like I told the AC tech today, if you can read and follow directions, then you can pretty much do anything. In saying that, I’m not a fool. I’m not going to really attempt something that I have no knowledge with like going outside and changing an AC capacitor. LOL. I know my limitations. Thanks for the comment!!

          • 9

            I have another update and hopefully this will be the last one. I had to call the AC tech again Saturday because my unit had stopped cooling. He thought it could probably be the blower and then told me that I must have done something wrong with wiring the thermostat. He asked me where I put the G wire, etc. Now, grant it, it was working when he replaced the outside capacitor. Anyway, I texted him a picture of the model and serial numbers so he can pick up the parts before coming to the house. So he told me that it was the capacitor. He said the unit has an outside and inside capacitor and that lightning could have hit it. So, the house is cooling again. Thank God!! I did tell him that he hurt my feelings for saying that I didn’t install the thermostat correctly. He laughed and said, “No. You did do a good job and that most women wouldn’t do it or let alone touch it.” LOL. I hope this helps you all. Be blessed!!

          • 10

            Oh, he only charged me $35, the price of the part since he charged me labor on Friday. Praise Jesus!!

          • 11

            After waiting a couple days to confirm that this will be my last comment, I can now tell you that I had to call the AC tech out again because the unit kept freezing up on the inside although the outside pipe was showing frost on it; however, the unit was still on outside but not inside. After I would let it thaw for a couple of hours, when I turned the system on it would make a stirring sound but wouldn’t start, I would then flip the main AC switch on the unit to the off position (not on thermostat), wait a few seconds and flip it on; the unit would start. The AC tech checked the blower and said everything looked good and didn’t know what it could be. When I told him what I had to do to start the unit, he said that it could be the relay switch to the unit. He changed it for free and called me later that evening to see if it was working. It’s been a couple of days since then and everything is working perfectly. Thank God!! He did tell me that the capacitor still had to be changed because the unit was working outside. I hope this helps someone. Be blessed.

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