wiring thermostat


Old 10-12-07, 11:16 AM
Thread Starter
Join Date: Oct 2007
Posts: 1
Question wiring thermostat

I'm trying to install a new thermostat, but my brain fart due to not eating caused me to unhook the existing one without marking the wires. Does anyone know what wires may go to where. I have a Blue, Yellow, Red, and Green. My possible connections according to the instructions are Rh=heat pwr supply, Rc=cool pwr supply, W=Heat signal, Y=cool signal, and G=Fan. There's a prexisting jumper from Rh to Rc on the new thermostat. It's a Honeywell RTH230B.

If I wanted to use a multi-meter, what would I be looking for?

Any help would be appreciated, thanks!

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Old 10-12-07, 11:30 AM
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Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,335
The blue wire is strange, thermostat wire is usually white, red, green, yellow. What type of heating equipment do you have? Do you have an air conditioner?

In the typical case:
red = power supply
yellow = cool signal
white = heat signal
green = fan signal
Old 10-12-07, 11:37 AM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Why not try looking at the other end of the wires, at the furnace, and see where they are connected.
Old 10-12-07, 11:41 AM
Join Date: Mar 2006
Location: NE Wis / Paris France{ In France for now }
Posts: 4,808
Most thermostat cable i useally know they come in 2 ,4 ,5 and 7 but very rarely 9 conductors

i will list the most common colours

Red/white stripe

sometime may have other colour combo as well if not in the list but it do crop up once a while

Normally the Red is power supply [ typically 24 volts ac ]
yellow for cooling
white heat
green fan
the additonal color will used on heat pump or muti stage units[ it will varies a bit but i will post the most common ]

orange for back up heat
bleu second stage [ both heating and cooling stage]
but keep in your mind some HVAC may wired with diffrent set up my best bet is check the control panel on the furance or air handler unit

that will useally give you a head up how it ran

Merci, Marc

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