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RTH7400 thermostat installed-screen display unlit-used page 10 wire installation. Used heat pump wiring-which does not show W2 and Y2 on heat pump schematic, so used conventional displayed W2 and Y2 connections. Have heat pump w/elec. furnace backup. Suggestions??

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  • Anonymous Mar 19, 2014

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W2 and y2 are used for 2stage applications

w2 = 2 stage heat
y2= 2 stage cool

If your system is a single stage system, look for the y1 and y2 terminals. If the thermostat does not have y1 and y2 then you may have the wrong thermostat. As always, please read the directions carefully. Thanks!

Posted on Jul 03, 2008

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Can you provide me with the wiring instructions, I want to replace the old analog thermostat. I have a roof mounted not ducted Advent A/C and a furnace unit.


The terminal board on the rtu should match fairly closely with the letter designations on the thermostat. R, W ,(possibly W2) G, Y, (possibly Y2) and C. W2 and Y2 are most likely NOT used on a small capacity rtu (roof top unit) as those terminals are for a second stage of heating and a second stage of cooling.

The thermostat terminals should be Rc, Rh, W, G, Y and C (common). IF the replacement thermostat is programmable the common terminal should be used because that allows the thermostat to run on 24vac and not just battery power.

There should be a factory jumper installed across Rc and Rh and that should stay in place as the two terminals are for systems that have TWO different control transformers. Small capacity rtu's will have only ONE transformer.

Some rtu's have a W2 terminal as well as a Y2 terminal even though they do not have the second stages of heat. You have to determine exactly what your system is prior to changing the thermostat.

Apr 14, 2015 | Air Conditioners

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Thermostat wiring terminals and colors


R - The R terminal is the power for the thermostat. This comes from the transformer usually located in the blower section for split systems but you may find the transformer in the condensing unit. For this reason, it is a good idea to kill the power at the condensing unit and the blower section before changing or working on the wiring at the thermostat. If you have a package unit then the transformer is in the package unit.
Red for the R terminal.

RC - The RC terminal is designated for the power for cooling. Some HVAC systems use two transformers. A transformer for cooling and a transformer for heating. In this case the power from the transformer in the blower section would go to the thermostat terminal. It should be noted that a jumper can be installed between RC and RH for a heating and cooling system equipped with a single transformer.
Red for RC terminal.

RH - The RH terminal is designated for the power for heating. See RC above for an explanation. It should be noted that a jumper can be installed between RC and RH for a heating and cooling system equipped with a single transformer.

Y - This is the terminal for cooling or air conditioning and goes to the compressor relay. Typically a thermostat wire pull is made to the air handler on split systems and then this wire is spliced for the separate wire pull which is made to the condenser. Some manufacturers put a terminal board strip near the control board in the air handler so a splice is not needed.
Yellow for Y Terminal.

Y2 - This is the thermostat terminal for cooling second stage if your system is so equipped. Many systems only have a single compressor but if you have two compressors which should only operate off of one thermostat then you need the Y2 thermostat terminal for second stage cooling.
*The most common color I've seen used for this terminal and wire designation is light blue but this varies and is completely up to the installer what color to use. Most installers use the color coding as noted but be aware that some do not use the thermostat color coding.

W - This is the thermostat terminal for heating. This wire should go directly to the heating source whether it be a gas or oil furnace, electric furnace, or boiler,
White for W Terminal.

W2 - This is the thermostat terminal used for second stage heat. There are gas furnaces with low fire and high fire and some depend on control from a two-stage heating thermostat with a W2 terminal. Heat Pumps use staging for auxiliary heat and need a W2 terminal.
*The most common color I've seen used for this terminal and wire designation is brown but this varies and is completely up to the installer what color to use.

G - This is the thermostat terminal used for the fan relay to energize the indoor blower fan. On a split system the blower fan is in the blower section while with a package unit the blower fan is in the outdoor package unit.

Green for G Terminal.

C - This is the thermostat terminal which originates from the transformer and is necessary to complete the 24 volts power circuit in the thermostat but only if the thermostat consumes electricity for power. Many digital thermostats require 24 volts for power so the common wire is necessary.
C stands for common and there is no universal color used for this terminal although black is the most common color I've seen.

O or B - These thermostat terminals are for heat pumps and the B thermostat terminal is used on for Rheem or Ruud and any manufacturer that energizes the reversing valve in heating mode for the heat pump. Most other manufacturers of heat pumps will utilize the reversing valve for cooling and the O thermostat terminal will be utilized for this purpose. This wire goes to outside heat pump condenser where the reversing valve is located.

Orange for O and Dark Blue for B depending on the installer of the heat pump and the manufacturer. If you have a Trane, Carrier, Goodman, Lennox, Ducane, Heil, Fedders, Amana, Janitrol, or any other manufacturer other than Rheem or Ruud you will be utilizing the orange wire for reversing valve. Rheem and Ruud will usually utilize the blue wire for reversing valve.

E - This thermostat terminal is for heat pumps and stands for Emergency Heating. If for whatever reason the heat pump condenser fails and it is necessary to run the heat there is an option on heat pump thermostats for emergency heating. Basically this simply utilizes the back-up heat source many heat pumps have to heat the home without sending a signal to the condenser to run for heat.

E - There is no universal color used for this thermostat terminal designation but this should be wired directly to the heating relay or the E terminal on a terminal strip board in the air handler or package unit if you have a heat pump package unit.

X or Aux - This thermostat terminal is for back-up on a heat pump and allows for auxiliary heating from the back-up heat source usually located in the air handler.

X or Aux - There is no universal color used for this thermostat terminal designation but this should be wired directly to the heating relay or the Aux terminal on a terminal strip board in the air handler or package unit if you have a heat pump package unit.

S1 & S2 or Outdoor 1 and Outdoor 2 - Some thermostats have this terminal and it used for an outdoor temperature sensor. The wire uses for this should be special shielded wire and completely separate form the other thermostat wires.







on Jun 06, 2011 | Air Conditioners

1 Answer

Carrier OEM to Honeywell Programmable Tstat - NEED HELP


you likely have a "two stage" system, but not a two stage heat pump. the first stage is probably the heat pump itself, and the second stage is the auxilliary resistance heat that suppliments the heat pump at lower temps. if i knew the terminals that are available on the new stat, i could advise you on the proper wiring.

Jan 27, 2013 | Carrier Air Conditioners

1 Answer

How to set a NOMA HTM311A thermostat


Go to the furnace, and see what the black is connected to. If it is not the Y terminal, disconnect it from the Y terminal at the thermostat. While you have the furnace open, check for a blown fuse inline to the transformer or on the control board. If the black was connected to the common or the transformer, and you connected it to the Y, and turned the thermostat to cool, you would have a direct short across the transformer output. You can use a black wire to control the A/C, but both ends need to be connected to a Y terminal.

If you still remember the where the 4 wires were connected to the White Roger thermostat, take note of the name of the terminals the 4 wires are connected to. That may help as sometime the colour of the wires are not always correct.

Or you really want to test it out:
connect RED wire to GREEN wire should turn on the fan
connect RED wire to WHITE wire should turn on the heat


Did you disconnect the power at the furnace first? Maybe you blew a low voltage fuse.

Make sure you increase the heat setting to go above the room temperature.
Thermostat wire color codes explained.
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).


Hope it helps.


Thanks for using fixya.....

Nov 29, 2010 | Air Conditioners

1 Answer

Just removed a lennox system and installed a RTH7600 put the Blue wire on C, the green wire on G the Yellow wire on Y, the Orange wire on W, the Red wire on R, the white wire on W2, Brown wire on Y2 and I...


you need to trace wires orange is where your prob is. it goes on o or b for reverse valve. w is 1st stage heat which should be wht and eletric heat should be w2 unless you got to compressors you dont need y2 please give me a vote and rating

Sep 21, 2010 | Air Conditioners

1 Answer

Replaced Bryant T-stat model TSTATBBNB001 with Honeywell t-stat


Hello,You forgot to wire the O terminal w1 witch is the reversing valve.It is important to check if old stat is using O or B in witch case B terminal=w1 leaving O unused.

Apr 21, 2010 | Honeywell Air Conditioners

1 Answer

Wiring Trane/Honeywell TH8320U


use the outside designations for heat pump, and inside for standard, I would assume a heat pump since you have more than five wires attached to it now. Use the colors of the wire to match to the designations, use tan for y2, black for w2 rc and rh should already have a factory jumper. I would have to trace out the "U" and see where it terminates, I have not seen a bare wire on a stat in 27 years of doing this. before powering, verify the tan and black at the indoor unit circuit board and see if they are landed on the terminals designated at the stat. hope this helps

Jul 27, 2009 | Air Conditioners

1 Answer

Thermostat wiring


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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).

Jun 02, 2009 | Carrier Air Conditioners

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...


Normal 0 MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman";} Thermostat wire color codes explained.
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 | Air Conditioners

2 Answers

I have a Ruud thermostat want to change to totaline p274-0200-c


what are the choices on the new t-stat need to know that first

Nov 23, 2008 | Ruud UBHC Air Conditioner

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