I removed my old round dial thermostat and did not label the wires. It's a 5 wire system. When I went to install the new Honeywell digital thermostat I realized I didn't know which wires went where. I have these color wires - Blue, Red, White, Green, Yellow. The digital thermostat has places for Rh, Rc, W, G, Y. I tried it, and started the heat, but cold air is coming out of the vent. If the colors are to match up, then where does the blue wire go? Please help! Thanks! :)

I seem to be having a similar problem. Mine is a 4 wire system and I purchased a Noma thermostat. I currently have White,Green,Blue and Red wires. Based on the advise I got online so far, I've bridged the Red and White wires and I'm getting the heat. This is just to test and make sure that the furnace is OK. May be you can do the same test but still needs somebody who knows the wires to tell us where the wires should fit in to, especially the Blue. Please let me know if you find a solution soon.

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 Auxiliary 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).

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Originally Posted by kvangel

I removed my old round dial thermostat and did not label the wires. It's a 5 wire system. When I went to install the new Honeywell digital thermostat I realized I didn't know which wires went where. I have these color wires - Blue, Red, White, Green, Yellow. The digital thermostat has places for Rh, Rc, W, G, Y. I tried it, and started the heat, but cold air is coming out of the vent. If the colors are to match up, then where does the blue wire go? Please help! thanks!! :)

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I did not label the wiring before I remove the thermostat , the old thermostat is a rheem.
The new is honeywell heat pump