# Honeywell / Honeywell thermostat replacement question.



## FatBear (Jan 14, 2009)

Hi,
I have a WaterFurnace geothermal heat pump system and a Honeywell Chronotherm III thermostat. (I think that's a pretty old model.) I believe the thermostat is acting up, so I bought a new Honeywell RTH6450D to replace it. I figured Honeywell to Honeywell should be easy enough. Wrong. At least so far. 

The problem is that my old thermostat has a "C" terminal with a blue wire connected to it. The new thermostat does not have a "C" terminal and the wiring instructions actually say "do not connect". Is there some explanation as to what this wire does and why the new thermostat might not need it? (I would think that the furnace determines what wires are or are not needed, not the thermostat.)

Naturally, Honeywell's consumer help line is not open during the hours that most consumers are at home.

Did I get the wrong thermostat? Or should I get a different brand entirely?

Thanks for any help I can get. It's cooling off as I write this... 

--FatBear


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## Houston204 (Oct 18, 2009)

Your new stat runs on batteries. It will work as long as you remember to replace the batteries annually.

The Honeywell RTH7600 has a C terminal if you do not feel comfortable with batteries powering your stat.










Color codes vary.


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## FatBear (Jan 14, 2009)

So the "C" terminal is a power supply from the furnace? In that case, I wouldn't care if I couldn't re-connect it. Maybe I should check the furnace end and disconnect it down there, too?

Hmmm, the old thermostat has batteries and the "C" wire hooked up. Were the batteries just there for backup?


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## Houston204 (Oct 18, 2009)

> So the "C" terminal is a power supply from the furnace?


Yep...... R and C are the 24 volt power circuit.



> Maybe I should check the furnace end and disconnect it down there, too?


I would.



> the old thermostat has batteries and the "C" wire hooked up. Were the batteries just there for backup?


Yes......


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## FatBear (Jan 14, 2009)

Thank you very much, Houston204!


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## FatBear (Jan 14, 2009)

Oh boy, naturally it was not so easy. First, when I went to disconnect the blue wire at the other end, I found that it connected not to one but to two places in the furnace. I clipped it off where it goes into the thermostat wiring bundle, but left room to strip and reconnect if necessary. Good thing, too because ...

I removed the old thermostat and marked all of the wires. I screwed the base plate of the new one to the wall. I was getting ready to connect the wires to the new one when I read a little note at the bottom of the wiring page of the install manual: "If your old thermostat had Y1, W1, and W2 wires stop now and contact a qualified contractor for help." For cryin' out loud! They're both Honeywell thermostats and both supposedly have the same functionality, why can't they make their own models compatible with one-another?

OK, so here is how my old one was wired (just the wires in question):

1. Y1 and W1 screws are jumpered with a factory buss bar and the yellow wire from the furnace was connected here.
2. E and W2 screws are jumpered with a short piece of white wire and the white wire from the furnace was connected here.

The new thermostat has (in addition to the others) E, Aux, and Y terminals. It shows the following old wire designations going to these terminals:

1. E wire goes to E terminal
2. W1 / W2 wire goes to Aux terminal (but it doesn't say if that means "W1 AND W2" or "W1 OR W2".
3. Y1 wire goes to Y terminal.

Another note says "If E and Aux terminals do not each have a wire connected, use a small piece of wire to connect them to each other.

So what do I do? Any help will be very much appreciated!


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## FatBear (Jan 14, 2009)

What would happen if I just jumpered E and Aux terminals and connected the white wire there, and connected the yellow wire to the Y terminal?


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## hvactech126 (Nov 11, 2010)

What color wire went to what terminal on the old stat. Honestly this has already been answered for you and you are making it harder than it is. Answer my question and I will list it out in simple terms for you.
EXAMPLE :
Old = Color = New
R = RED = Rc/Rh


BTW, I would use C on the new thermostat!


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## FatBear (Jan 14, 2009)

I don't know how thermostats or heaters work inside, so I don't know what happens if I connect something wrong. And I do want it to work correctly. So I am concerned about the warning in the manual for the new thermostat.

Here is my chart:

Old = Color = New
R = Red = R
O = Orange = O/B
G = Green = G
C = Blue = ??? (there is no C terminal on the new thermostat and the manual does say "do not connect")
Y1 + W1 = Yellow = ??? (+ sign means they were jumpered on the old one) 
E + W2 = White = ??? (+ sign means they were jumpered on the old one)

The new thermostat has the following terminals in all:

L E Aux G O/B Y R Rc (R and Rc are already jumpered.)


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## hvactech126 (Nov 11, 2010)

Yes, I apologize, Houston normally uses a image of the stat you are installing. This time he did not do that.

Old = Color = New
R = Red = R + Rc
O = Orange = O/B
G = Green = G
C = Blue = not used - tape off or disconnect like you have already.
Y1 + W1 = Yellow = Y
E + W2 = White = Aux + E

Installer options :
1 = 5 
2 = 0
3 = 1
6 = 3 TRUST ME
8 = 3 TRUST ME
12 = 0
13 = 1
14 = 0


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## FatBear (Jan 14, 2009)

Got it. Thank you! (Now maybe I can warm this place up.


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## hvactech126 (Nov 11, 2010)

see previous post - updated


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## FatBear (Jan 14, 2009)

I appreciate the additional help. I got it all wired up and the durned thing wouldn't run. I might have seen those additional settings in the book after sleeping in the cold over night. But thankfully I saw your updated post with the installer settings and changed them accordingly and now it is running and generating heat. I am happy, the wife is happy and the skinny little dog is extremely happy.


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## Danman0622 (May 5, 2014)

I think honeywell is subsidizing the battery industry by placing the words do not use on the c terminal. I connected the common to that terminal and what do you know, it turned on without batteries. I don't know why it would say do not use if it works with the common.


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## hvactech126 (Nov 11, 2010)

Danman0622 said:


> I think honeywell is subsidizing the battery industry by placing the words do not use on the c terminal. I connected the common to that terminal and what do you know, it turned on without batteries. I don't know why it would say do not use if it works with the common.


That is because it is the retail version and most consumers get confused by the C terminal and miswiring with it can cause harm to your hvac system.


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## Danman0622 (May 5, 2014)

Blown transformer


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