About to install a new Honeywell RTH6300B thermostat. I have 4 wires coming from the wall... green, white, red and blue. Old thermostat had connections for W, RH, B, RC, G, O, Y... (Old thermostat was White Rodgers model # 1F86-244.) New Honeywell RTH6300B thermostat has connections marked G, W, Not Used, Y, R, Rc.

I can understand Y=yellow, W=white, G=green, and R=red... what about the blue wire? New Honeywell thermostat has no terminal labeled B.

P.S. Old thermostat (White Rodgers) had a red metal jumper on RH and RC with the red wire from the wall connected to the RC terminal.

New Honeywell RTH6300B thermostat has a metal jumper on R and Rc.

Any help would be greatly appreciated.

This original post was edited Friday Aug 18, 2006.

Doubt that the blue was hooked up before if it's an older system. Hook it up using the yellow only.. You only need 4 wires to the stat... Either the yellow or the blue will go on the "Y" terminal... I vote yellow...

You should check to see if you have a heat pump system, which appears that you do, and the new stat is not compatible with heat pumps.

I don't have a heat pump system. My A/C is brand new (few weeks old... Trane XR13) and my heating system is only 6 years old (gas furnace central heating system).

Look at the terminal bar inside the furnace where all of the control wires are connected. You should have a post marked C on this post oill be one of the wires going to the condensing unit out side You will have a post markied Y on this post you should have the other wire that goes to the outside unit also on that same post you will have one other wire it will be blue or yellow. If it is yellow use the yellow wire at the thermostat to connect to the Y post, if the wire is blue then use the blue wire on the Y post. The others should be color coded red to RC, white to W and green to G, leave the junper wire between the RC and the RH,

I made a mistake in my original post. I have 4 wires coming from the wall NOT 5 wires. The colors are White, Green, Blue and Red.
Original post has been corrected as of Friday Aug 18, 2006.