DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   HVAC (
-   -   help with thermostat wiring (

happyneko 06-14-2012 10:38 AM

help with thermostat wiring

A couple of weeks ago we had an issue where our AC wouldn't turn off. We had a guy come out and he said there was a short in the yellow wire, and that he could either run a new wire (probably a couple of hundred for them to do it) or just use my blue wire for the yellow. I had him just use the blue wire and figured i'd run the wire myslef. I actually use my blue wire for a C wire for a z-wave controllable thermostat i have so i didn't want to just leave it this way.

So I've run the new wire, but a bit confused about how to go about hooking everything back up. Here is a picture of my current thermostat (a temporary honeywell one because i had removed my old themrostat thinking it was the problem) I'm not sure why the white wire is disconnected, but you can see teh blue is in the Y spot.

In my boiler room, I found where all the wires are connected, and there is a 3rd cable with just a red and white wire. I assume this goes either to the AC unit outside, or maybe my attic fan? anyway, i drew how the wiring is done. The yellow wires are just hanging free not connected to anything

Finally here is a picture of where teh wires terminate in the furnace

What i'm confused about is if the blue wire is being used as the yellow now, shouldn't it terminate in teh Y spot in the furnace?

So now that I have the new wire, should I

1. put everything back to it's normal spot in my old z-wave thermostat. Blue in C, Yellow in Y, Red in R, Green in G, and white in W.
2. In the boiler room, hook the yellow wires up how the blue ones are currently with the the other red/white mystery wire, and just connect the 2 blue wires together directly?

Doc Holliday 06-14-2012 04:24 PM

Is anything working, such as cooling?


Y-yellow (or blue if yellow is broken)

Boiler/furnace to stat:

Y-yellow (or blue if yellow is broken)

Other cable is to the outside a/c condenser which is hooked up at the furnace:

either color, red or white to the Y terminal (which means you'll now have two wires on that one terminal, one going to the stat and one going out to the condenser.

other wire to the C, common. Done.

Doc Holliday 06-14-2012 04:25 PM

I'd also suggest you clean up those wires in the stat. They appear to show too much metal.

gregzoll 06-14-2012 05:41 PM

A hundred dollars to pull wire, that is pretty much all labor. How hard would it be for you to just pull all new wire? I would pull at least 10 or 12 wire #18 to the thermostat.

You would just attach either a pull strung, or the new wire to the old, and have a helper help to keep it from tangling.

BYW, what thermostat are you using?

happyneko 06-14-2012 05:48 PM

the cooling is working fine right now, i assume the heat is too but i havn't tried it. I'd leave it this way except I want my blue wire back so i can hook up my 2gig z-wave thermostat again to remotely c ontrol

I've already run the new cable, i was just confused bout how exactly to hook it back up correctly after he'd done the modification.

gregzoll 06-14-2012 05:53 PM

Just match the colors to the terminal. Y is yellow, R is red, B is blue, W is white, G is green, etc..

happyneko 06-14-2012 05:54 PM

should it be hooked up like this in the end?

gregzoll 06-14-2012 06:06 PM

The wire from the A/C should connect at the board in the furnace, and the wire from the thermostat should connect to the board in the furnace. Forget about that drawing, it is just going to confuse you and the next guy.

happyneko 06-14-2012 08:47 PM

the wire from the ac doesn't reach the furnace board. i'm pretty sure it never did and was always interconnected midair.

if it did though, the red and white wires shouldn't go to the R and W terminals should they? or else why are they connected to blue right now (which goes to Y on hte thermostat)

gregzoll 06-14-2012 09:30 PM

Can't you pull new wire for the a/c to the furnace, or just run a length from where it ends, to connect to the furnace. For the Air conditioner, the wire could be Blue & yellow, it could be Red & Green, it could be Yellow & Black. It matters what terminals it connects to on the furnace, just not the colors. One wire from the a/c connects to 'C', the other to 'Y' on the furnace board. Just doesn't matter what color where, just as long as you connect it properly to the furnace, so it will run when it gets a call for a/c.

happyneko 06-14-2012 09:54 PM

ah ok. does it matter which wire goes to C or which to Y? or as long as you have one to each the circuit is happy?

thanks a lot fo the info

gregzoll 06-14-2012 10:07 PM


Originally Posted by happyneko (Post 943720)
ah ok. does it matter which wire goes to C or which to Y? or as long as you have one to each the circuit is happy?

thanks a lot fo the info

Again, no it does not matter what color goes where. Some people have a preference, but if you look inside the outside unit, you will notice that the two wires are the same color at the low voltage side of the contactor. On mine they are yellow, but the wires from those to the furnace are Red & White. Again, it does not matter what color goes where from the a/c to the furnace.

All times are GMT -5. The time now is 08:28 PM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

Search Engine Friendly URLs by vBSEO 3.6.1