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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I am installing a new thermostat to a Nordyne furnace. There

Customer Question

I am installing a new thermostat to a Nordyne furnace. There are 4 wires coming to the thermostat red, white green and black. Thermostat is a Honeywell RTH6400D with contacts labelled G, W, Y, R&Rc(jumpered).
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: How do i connect them
JA: Do you plan on doing the work yourself?
Customer: yes
JA: Anything else we should know to help you best?
Customer: i've turned furnace off. I've done the same thing a few years ago in our previous home.
Submitted: 4 months ago.
Category: HVAC
Expert:  Rick replied 4 months ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. First I’ll need some more info so I have a more complete picture of your situation.

Did you label the wires before you removed the old thermostat?

Expert:  Rick replied 4 months ago.

I can't answer your question unless I know what the situation is with the existing wiring. I can give you the standard color coding but it's not always followed

Customer: replied 4 months ago.
I haven't disconnected. They are still connected to the old thermostat (also a Honeywell). It has two connection blocks. The right side has terminals R,Rc, W, Y,G,C and the left block has Y, W2, K, S1 and S2. The connections are:
White wire goes to R,Rc(jumpeered), White goes to W, Green goes to C, and black goes to the K on the other side?
Customer: replied 4 months ago.
This is beginning to look like a money scam.
Expert:  Rick replied 4 months ago.

Do you have central AC? Your old thermostat has 2 white wires and a K terminal??

Customer: replied 4 months ago.
I have central air. I already told you the letters of the terminals in the old thermostat. But there are only 4 wires as I've already told you. So what else do you need to know??
Expert:  Rick replied 4 months ago.

First of all I've never seen a K terminal on any honeywell thermostat, next if you have central air it won't work unless you have a wire on the Y & the G terminals. I'm completely blind here except for what you tell me and so far it doesn't add up.

Customer: replied 4 months ago.
Neither did technicians at Home Depot which is why I decided to try Just Answer. I know the standard connections are Y for compressor, W for heat, G for furnace fan and R for 24v supply. But I thought there would be someone who could tell me why C and K are connected? If you don't know then I'll just ask for a refund. thx
Expert:  Rick replied 4 months ago.

I'm going to open this up to my colleagues so one of them can help. Please don't respond (even to acknowledge this post)until you get a response from us. If you respond first it will only delay your answer.

Expert:  Phil replied 4 months ago.

Hello,I am a retired mechanical engineer with 56 years in this business. I will go in depth with you, and up to a 6 hour time limit.

All I ask is please select the ***RATING LINK*** at the top of your page before leaving, that is the only way I am credited through the site.

Rating does not affect your charges nor ability to refund if not satisfied. If you can agree to that, lets continue by all means.


Just Answer is not a scam to say the least, its a huge company with thousands of experts including doctors and lawyers.

The problem is that the wire colors used are not the standard colors.

Green should go to G (not C) on the thermostat and on the thermostat terminal strip in the furnace... that is the first thing to confirm


IF however Green goes to C at the thermostat terminal strip, as well as C on the thermostat, we can make that work.

Lets verify that first.

Next tell me where the black K wire connects inside the furnace.

We can go from there

Expert:  Phil replied 4 months ago.

I need a close up photo of the wiring diagram glued inside the furnace blower access panel, it must be exceedingly well focused, attach it here using the 'add files' link next to your send button.

I also need a clear photo of the printed circuit board mounted on the blower inside the furnace, photo must show the thermostat wire connections clearly.

Customer: replied 4 months ago.
I think I've figured it out. I moved to this house a year ago and the thermostat quit a few days ago. It was quite different to any I had seen and I've just noticed a label that says 'Peak Saver' This was a program of the utility company that gave you a free programmable thermostat and discounted hydo rates so long as you agreed that they could cut your service during brown outs. The thermostat must have had the strange terminals so they could cut your service when needed.
I've just looked at the terminal board inside the furnace. It uses the standard R,C,Y,G,W.
There is something unusual however The C terminal has a white and blue wire connected; the Y terminal has black and yellow; Green to G; and white to W. The black wire and one of the white wires are from a different cable . I'll attache two photos; the first (153907) is the terminals inside the furnace, the second(91855) is the old thermostat wiring.
Remember that the 4 wires coming out of the wall at the thermostat are Red, White, Green and Black. Am I safe to connect the new thermostat using standard convention?
Expert:  Phil replied 4 months ago.

I will wait for the photo.s

Expert:  Phil replied 4 months ago.

I got the photo's now

Expert:  Phil replied 4 months ago.

- Green goes to G on the thermostat NOT C

- Blue from the circuit board goes to C on the thermostat...I do not see blue wire at your thermostat though so an illegal splice was made, no telling what the details might be on that.

- Yellow wire should go to Y on the thermostat but I do not see a yellow wire at the thermostat.

This system has been messed up by an unqualified technician not using the standard wire colors...

You will be best off calling in a qualified HVAC outfit to inscramble that mess for you, from here it is not possible for me to check for those color change splices. For the record this is not an answer, you may ask for a refund of your deposit if you like.

Customer: replied 4 months ago.
Thanks Phil. I should have gone to an HVAC contractor - I did try, but I coupld not get one until next week. I guess I'll just have to wait.
I will ask for a refund but I do appreciaete your honest reply.
Customer: replied 4 months ago.
i don't want another technician. Just a refund and cancellation of my trial membership.