I have a 4 wire system coming from the wall. Blue, green, red, white. Im am installing a new programmable thermostate by Honeywell. I have 5 options to lable and hook up the wires correctly they are Rh, Rc,W,Y,G. The wires are not labeled and its an older home. I just don't want to hook it up incorrectly. The old thermostate was a round dial and had letters to correspond with the wire. Are for red , W for white, G for green but B had no letter. I need a little help. Got any suggestion ?

Put a jumper wire between RH and RC red goes to RH, Green goes to "G", white goes to "W", blue should go to "Y"

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Originally Posted by japritc

I have a 4 wire system comming from the wall. Blue, green, red, white. Im am installing a new programmable thermostate by Honeywell. I have 5 options to lable and hook up the wires correctly they are Rh, Rc,W,Y,G. The wires are not labled and its an older home. I just dont want to hook it up incorrectly. The old thermostate was a round dial and had letters to correspond with the wire. R for red , W for white, G for green but B had no letter. I need alittle help. Got any suggestion ?

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Your 4 wire t-stat is likely wired like the first schematic here:

Thermostat wiring code

Rh and Rc should be jumpered together and called R.

I don't know your skill level or what tools you own (multimeter? can you make a test light with a resistor+diode+LED?)

You can always look at the furnace end which is recommended, but beware some BOZO can always switch wire colors in the wall.