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Installing a stat to a furnance

Need step by step on installing a thermastat to a two stage heating and cooling unit. I have installed a five wire line, or do i need more lines.

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You need a 7 conductor minimum, 8 will suffice.

Depending on what type of thermostat you are using, hard wired or battery will make a difference, some model thermostats have a "C" on the terminal strip regardless of the power being supplied to the thermostat. If your Thermostat does NOT have a "C", and the furnace does not require a common, then disregard that terminal.
The Terminal strip on the thermostat and the terminal board on the furnace should be close to this, and let’s assume you have 2 stages of cooling as well. This is a general rule of thumb for the wiring and their correct place.

R - 24VAC
W - Heat
G- Fan
Y - Cooling
W1- Stage 2 Heat
Y1 - Stage 2 Cooling
C - Common

Posted on Dec 02, 2008


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Jan 27, 2013 | Carrier Heating & Cooling

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I have a Honeywell LR1620 Thermostat that I am replacing with a Honeywell RTH230B. I se where all the wires go to on the new thermostat EXCEPT the blue wire that is attached to the "W2" terminal...

If your old t-stat had a W2 terminal with a blue wire connected, and your new t-stat does not have a W2 terminal, then you may have purchased the wrong t-stat. The old is a 2 stage heat where your new is a 1 stage heat. 2 stage heat means the tstat will engage 2 heat elements, then if it continues to get cool inside, the Tatar will engage w2 and the remaining 1 or 2 heat elements. If you want it like it was to begin with, you'll need a 2 stage heat 1 stage cool tstat.

Oct 10, 2017 | Heating & Cooling

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I have a carrier 38YC(M) heat pump and trying to install a programmable t stat (honeywell RTH6350D). One of the setup steps asks what kind of pump it is: with out without backup or auxillary heating,...

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Jun 12, 2011 | GE Heating & Cooling

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I installed a new Honeywell Programable thermostat, When I turned on the AC it turned on the Heater... I followed the wiring but some of it is not making sense... G=Green, Y=Yellow, R=Red, C=Blue,...

Hi, the problem is you have bought the wrong thermostat for the unit if it is not a heat-pump. A heat pump will have W-1, W-2 for heat strips, and Y-2 is for 2nd stage cooling. G is Green for Fan, R is Red for Power, Y is Yellow for cooling, and W would be for Heat. This is all you need if you have gas heat, Orange is for a reversing valve for a heat-pump, and the blue is also for the reversing valve on a Rheem heat-pump. The stat you need will have these terminals, if you are sure its not a heat pump, which I am sure you would know. The stat you need has these terminals. RC and RH. It will have a Red jumper wire connecting the 2 terminals. This is where the Red wire connects, to either one, as they connect together. Connect G to Green, Y to Yellow, and W to white. Since you only have one control transformer, that's why the stat has RH for Red Heating, and RC for Red cooling tied together. Just hook the red coming in to either one. You need only, R, G, Y, and W, to run this unit. Look at your old stat and check the terminals. A heat-pump, uses many more conductors to operate it. O or orange for the reversing valve, blue also depending on the unit. C for common, W1 for stage one heating, W2 for stage 2 heating, Y1 for stage one cooling and Y2 for stage 2 cooling. This stat is used for a commercial unit with multible stages of heat and cooling. If you have a common wire and no batteries on the old stat, go to the indoor unit, remove the panel, and see if you have a common wire hooked up, such as the brown, black, or maybe blue. If so, you will need to hook it up at the stat if it has a C terminal. If it has batteries, just take all of the extra wires and shove them in the wall. You won't need them. Just the R, G, Y, and W, and you will be back on line. Very easy.
Please rate me. Take it back and have them sell you the right stat. Please keep me posted and I will be here if you need my help. Thank you for using Fixya.
A/C, and Heating Contractor

Nov 23, 2010 | Goodman Heating & Cooling

1 Answer

I am trying to install the new tx900ts in my house and i do not understand the wiring on it i have a old trane thermastat that has different wiring codes

common is different by installer so you gotta look at the units or you will blow out your transformer this wire will be blue or brown
24v always red
compressor always yellow
fan always green
reversing valve always orange
heat w1 always white
emergency heat will be either brown or black dependinting on installer if its a heat pump this it what you have but if its a gas system its much easier
red- 24 volt with a jumper already on the new stat
white- heat w terminal
yellow- cool y termina
fan green- g terminal
and common is optional with batteries so its not needed
if you need further help email

Sep 20, 2010 | Heating & Cooling

1 Answer

There is five wires yellow, green, red, white, the problem that we a facing is to connect these wire into the honeywell theromostat RTH3100C1002-0916

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Fuse Blows when diagramed wiring is used on GMP125-5

i would check your thermastat wiring if you blow the fuse you have a dead short those fuses are saving you alot of money. remove all wires from terminals for t stat on furnance and jump between r and w if it works your problem is in wiring ..........

Feb 26, 2009 | Goodman GMS90703BXA Heater

1 Answer

HELP!! I got a problem with my A/C

I looked at the pdf file page 20 of page 124 for t-stat says for a Y594g1476 to remove the jumper IF W1 is used. I don't know if you have 2nd stage of heat such as electric heat. I would check wiring according to your outdoor unit and indoor unit and the t-stat. At the very least you will need R and it looks like X terminal giving you the 24 volts. for the control circuit. O is for the reversing valve. G for the blower. Y for the compressor contactor. W1 goes to the fan section to operate 2nd stage heat if you have it.You can also remove the t-stat and make sure you have the correct subbase which the PDF file shows for a y594g1476 stat it should be a Q674 series. Also what you can do with the stat off is jump out R to G to O to Y that should bypass the t-stat and bring on the fan and compressor contactor and the reversing valve. ( reversing valve is energized in the cooling mode ) see what happens ,you may have a built in 5 minute timer before it starts.I was unable to find the PDF on your Tempstar. So I am not sure what the outdoor coil temp. sensor is. I know that to initiate a defrost heat pumps use an outdoor sensor strapped on the outdoor coil bend. it usually labeled DFT (defrost thermostat ) but that should only work in the heat mode. Also they may show an OPITIONAL outdoor sensor/stat to stage 2nd stage of heat if using electric heat. But as far as I know that is installed by the contractor and is optional. In closing I would double check the control wiring from the t-stat to the outdoor unit to the fan section. Then I would bypass the t-stat with the method I told you. You can also take it one step at a time R to G blower fan starts .R to O reversing valve energizes. R to Y compressor contactor closes (after 5 minutes).Also the PDF shows an optional outdoor sensor that hooks up to the thermostat. If your handy with a volt meter check that you have 24 volts between R and X terminal at the stat

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