Question about Honeywell CT87B ROUND HEATING&COOLING MECHANICAL THERMOSTAT - WHITE Heater

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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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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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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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Thermostat wiring on carrier furnace.How to??


you have to go to the furnace and match up the 4wire tstat wires to the thermostat so for instance say
RED-RED 24v
White-White heat
Green-Green fan
Blue-Blue will be Y for cooling

Nov 03, 2016 | Carrier Heating & Cooling

1 Answer

How can I make a thermostat connection?


Good morning Yakup.

The best way is to write down how the old t-stat was wired. If that's not available, the only way to determine for certain where each wire goes, is to check what the installer did at the terminals in your home comfort system. Please note the there is high voltage electric in each piece of equipment so if you decide to open up panels, there is always the risk of damaging the equipment or worse, injury or death if you are not a qualified service technician. However, typical color assignments are as follows:
R= (24v from heating appliance) Red
RC= (24v from cooling appliance) Red
These two are only separated when you have two different appliances providing seasonal comfort, like a boiler and an air handler. If you have a warm air furnace with an air conditioner or a heat pump attached then R+RC will have a jumper across them and only one RED wire will be landed there
W= (heat) White
Y= (cool) Yellow
G= (fan) Green
Those colors are pretty standard
The rest of the colors depend on availability in the jacket and are really up to the installer. You mentioned 7 wires but 8 conductors is more likely so I'm assuming the remaining colors are black, brown, blue, and orange.
I always use the following:
C= (common) Black
O/B= (reversing valve for a heat pump) Orange if the valve is energized for heat and Blue if the valve is energized for a/c.
Aux/E= (auxiliary or electric heat) Brown
L= I believe this is a diagnostic terminal for some systems with feedback data and is not used frequently.
After wiring there is some programing to do to set up your new thermostat to your type of system.

Hope that helps. God bless and be careful.

Aug 06, 2014 | Honeywell RTH6350D1000 5/2Day Prog...

1 Answer

Need help wiring this theromostat. I ahve the following color wires.....Green Red Black Blue White Yellow and Orange. Need to match them to the following connections: G RC RH Y/O W/B Y1


G= Green Wire (Fan) RC= Red Wire (Power Cooling) Y1= Yellow Wire (Cooling Contactor) RH= Black Wire (Power Heating) WB= White Wire (Heating Control) YO= Orange Wire (Damper Control)

Blue Wire is usually to C= Common

Nov 28, 2010 | Heating & Cooling

2 Answers

RED BLUE GREEN WHITE ARE THE FOUR WIRES THAT I HAVE TO CONNECT. PROBLEM IS THAT I FORGOT TO (AND I KNOW BETTER) MARK WHERE EACH CAME FROM TO PUT BACK IN THE RIGHT PLACE -- USED TO HAVE A DEHUMIDIFIER NOT...


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...

1 Answer

I tring to change thermosat I can not remeber what color go where


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)
COOLING ONLY Thermostat
R = Red One Side of 24 volt Transformer
G = Green Blower
Y = Yellow Cool
HEATING ONLY
R or Rh One Side of 24 volt Transformer
W = White Heat

Feb 09, 2010 | Heating & Cooling

1 Answer

Installing thermostat - extra wire?


you have to go down to your furnace and follow the thermostat wire ...it 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
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Nov 01, 2009 | Honeywell Electronic Programmable...

1 Answer

I need help with my central heat and air unit, it has a heat pump. the model number is GQ3RA-036K. I am changing the theromstat out and the wires are connected to it. there are eight wire colors that are...


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Please note. Not all installers use the proper color codes when they install or replace equipment. It may be necessary go go to the furnace or outdoor unit to verify what wires are for what purpose. Also be sure there are no splices in the wire that could change the wire colors between components.
  • R (red) or Rh (Red heat) 24 volts from equipment.
  • Rc (Red cooling) 24 volts from transformer in cooling equipment.
Note: If only furnace has a transformer and cooling equipment does not jumper Rc and Rh.
  • W (White) sends 24 volts to furnace control to start the heating cycle.
  • W2 (no standardized wire color, usually whatever wire color is available) controls second stage heat.
Note: W2 is most often used for heat pumps to control what is called emegency heat or Auxillary heat, and most often will use the white wire.
  • Y (yellow) often (blue) is used, controls cooling unit (outdoor condensing unit) also is used for heat pump heat.
  • Y2 (no standardized wire color, usually whatever wire color is available) controls second stage cooling.
  • G (Green) controls the fan "on" operation of the furnace/air handler. Also often is used to start the blower for many electric furnaces.
  • C (common) most often brown but can also be black or other color available to installer.
  • O (orange) Energizes heat pump reversing valve for cooling (Trane and most other brands).
  • B (Blue) Energizes heat pump reversing valve for heating (Rheem, Ruud and Weatherking).

May 07, 2009 | Heating & Cooling

1 Answer

Replacing the thermostat, took the old one off without marking the wires. Hooked it up by color and we get the furnace when we put it on cool. wires are green, red, yellow & blue (ground wire)on the...


the normal wiring for stats is white=w=heat,red=r=24volts,green=g=fan,blue=c=common,yellow=y=cooling.
see what ties into your furnace board and match the terminals.

Aug 12, 2008 | Honeywell Heating & Cooling

4 Answers

Replacing thermostat


What is the blue hooked up to now?

Jun 07, 2008 | Honeywell Electronic Programmable...

1 Answer

Changing thermostat matching wires trouble


Brown my friend is for the 4 way valve solenoid, that is if you have a heat pump, ( it uses freon for heating instead of natural gas) perhaps you got the wrong thermostat, if you have a brown you need a thermostat for a heat pump, a regular thermostat is not going to have a brown connection.

May 08, 2008 | Heating & Cooling

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