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Changing out home heating and cooling thermostat

I have thermostat wires: red, blue, green, and white. I assume I match the colors accordingly, but not sure of the blue wire if it connects to the y.

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Re: Changing out home heating and cooling thermostat

I have one red wire to connect to new thermostat that has RH and R/RC. Which of these do you connect too?

Posted on Jun 12, 2008

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Re: Changing out home heating and cooling thermostat

Yes, the blue or yellow are interchangeable. they are for the cooling mode. Just first make sure the white is heat, green is fan and red is the power 24v.

Posted on Dec 18, 2007

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On the back of your thermostat, you should have a R (Red), W (White), G (Green), Y (Yellow), and a C (Common). If you have a thermostat that also has a set up for a heat pump, you will have additional terminals, but you don't have to use them since you have a 4 wire, ( in case you do, make sure your thermostat is set up for 1 heat, 1 cool). Your wires are all color coded besides the blue. Red to R, Green to G, and so on. Your Blue wire is being used for Yellow which will go to the Y terminal. Blue is usually meant for a common, but with only having a 4 wire, that's the color that was used. Red is your power, Green is your fan, White is your heat, and Yellow is your A/C. Hope this helps clear some stuff up and good luck!

Mar 12, 2010 | Honeywell Electronic Programmable...


Thermostat Wiring and Terminal Designations

Here is a list of each common terminal and what their commonly used for. Also listed is what colors are commonly used. NEVER ASSUME these are what you have. Verify all your wires by following each to each piece of equipment. This will help you to be able to match your equipment with the terminal.

- R, Rc, Rh Red wire, hot side of transformer
- C various color wires Usually the common side of transformer
- Y Yellow wire, Energizes the compressor, cooling or heating and cooling for heat pumps
- W White wire, heating for most units
- G Green wire, energizes the fan or blower relay.
- O Orange wire, energizes cooling on most heat pump units
- B Blue and sometimes Orange wire, energizes heat on most heat pump units
- B or X Blue, Black, or Brown wire, the common side of the transformer when the t-stat needs a common. Some brands use B as the common (York, GE, and Trane)
- E Pink, Gray or Tan wires, Emergency heat relay on heat pumps with auxiliary heat
- T Tan or Gray wires, For units with outdoor anticipator reset control (Trane, American Standard, GE, and Carrier)
- W2 Pink, or Brown wires energizes second stage heating on 2 stage units
- Y2 Blue or Pink wires, energizes second stage cooling on 2 stage units
- L Can be most any color, energizes service indicator lamp on units that are equipped with that.

The wires that always cause the most confusion are the B and X wires.
Check out the B terminal first. The NEMA standard for the B terminal to be the heating changeover valve but with some units it is different.

Trane, GE, York and some other manufactures which includes older Honeywell thermostats often use it for the common side of the transformer.
“X” Usually is the standard for common, but just like “B” some manufactures do use “X” or “X2” as the terminal for the emergency heat relay.

on Dec 12, 2009 | Heaters

1 Answer

How do you wire a honeywell round mechanical thermostat

What are you trying to wire up?
Typical Thermostat Wiring for 4 or 5 wire Heat/Cool Thermostat (not heat pumps)
4 Wire Termostat
R = Red One Side of 24 volt Transformer
G = Green Blower
Y = Yellow Cool
W = White Heat
5 Wire Thermostat
with one transformer for both units
Rc One Side of 24 volt Transformer
Rh Jumper Rc to Rh
G = Green Blower
Y = Yellow Cool
W = White Heat
5 Wire Thermostat
With 2 transformers one for indoor unit
And one for outdoor unit
Rc = Red One Side of (outside) 24 volt (outside transformer)
G = Green Blower (outside transformer)
Y = Yellow Cool (outside transformer)
Rh = Blue One side of (inside) 24 volt (inside transformer)
W = White Heat (inside transformer)
R = Red One Side of 24 volt Transformer
G = Green Blower
Y = Yellow Cool
R or Rh One Side of 24 volt Transformer
W = White Heat

Feb 09, 2010 | Honeywell CT87B ROUND HEATING&COOLING...

1 Answer

I am tying to install an RTH6400 5 in 1 thermostat but the colors of wires i have on my wall are RED, GREEN, BLUE AND BLACK, where as the book has RED , YELLOW,WHITE AND BLUE. please which do i connect to...

You need to open up the panel at your furnace(air handler) and find the terminal strip and see what your existing thermostat wires are connected to. Normally your red wire connects to the R terminal(24 volts), the yellow wire to the Y1 terminal(cooling), the white wire to the W1 terminal(heating), the green wire to the G terminal(indoor fan). You can use whatever color of wire you have existing, just make sure that the R,W1,Y1,and G wires at the furnace match the R,W1,Y1, and G terminal screws at the thermostat. Also make sure the power to the furnace(air handler) is turned off before you make any wiring connections at the thermostat or furnace.This is very important! If you don't and you short any wires to ground(especially the R wire) you will possibly ruin the system step down transformer or blow the low voltage fuse.

Nov 10, 2009 | Honeywell Electronic Programmable...

1 Answer

Installing thermostat - extra wire?

you have to go down to your furnace and follow the thermostat wire connects to a terminal strip or fan centre...the color doesn;t really matter...installers mix and match all the time....look at the furnace wiring and mark it down...Red on "R"...Green on "Y" whatever it is...and connect it accordingly upstairs...if you only have 4 thermostat wires downstairs you will need a jumper wire between RH and RC...if you have 5 wires you will see 2 wires on "R" at the furnace.,...and connect either to RH and RC at the thermostat

Nov 01, 2009 | Honeywell Electronic Programmable...

2 Answers

Honeywell RTH230B works on AC not on Heat

check wiring to furnace check wire hook ups on board match letters and colors sometimes installer use what ever wiring they chose on letters

Oct 16, 2009 | Honeywell Electronic Programmable...

1 Answer

Can't match color wires to thermostat codes. I'm replacing my thermostat and I have 6 wires coming out of the wall but can't match colors to proper connections on thermostat. I have an electric heat pump.

Make sure you have a heat pump thermostat. Standard stat wire and stat wiring are as follows.
  • R to red
  • W to white
  • Y to yellow
  • G to green
  • O/B to orange
  • C to blue or W2 to blue
Your wire colors and stat brand and model number would be more helpful if this does not clarify. Repost with additional information and I would be glad to help further.

Oct 06, 2009 | Heaters

1 Answer

Replacing a Williamson (White Rogers) Termostat

rh is power for cooling terminal and rh is power for heating terminal connect red wire to rc or rh and there should be a jumper between rc and rh if not install one all other wires are color coded correctly. now the blue wire is not used.

Jan 05, 2009 | Honeywell Electronic Programmable...

1 Answer

Hot air does not come on

common color code is as follows:
Terminal Wire Color
W White
G Green
Y Yellow or Blue

This does not guarantee your thermostat was wired to common color code. Assuming it is a single transformer forced air heating and cooling system the following is likely your problem there should be a RC & a RH termial on your new thermostat incase you need a split sub-base for multiple transformers. My guess is that you are connected to RC, if there is not a wire to RH the heat function will not work. the thermostat should have been supplied with a jumper to connect RC & RH together for single transformer applications. If not any small gage piece of wire will work, if I have assumed incorrectly please give me more info about your system.

Dec 11, 2008 | Honeywell CT87B ROUND HEATING&COOLING...

4 Answers

Replacing thermostat

What is the blue hooked up to now?

Jun 07, 2008 | Honeywell Electronic Programmable...

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