I am trying to replace an old American Standard T8424C with a Honeywell rth7400. I am having the worst luck with the wiring scheme. I have looked at the unit itself to make sure the wires are connected to what I think are the right connections, but I don't know what to do with the white and blue wires.

The instructions say if my old unit used a w1 and w2 connection, contact an service man. I am trying to avoid this. It can be this hard to connect 6 wires.

Any help??

The American Standard used a color code G-B-R -W1(white)-Y-W2 (black). The directions on the honeywill are confusing. I don't know if I have to jumper anything (besides the r-rh) or what.

Any help would be good.

Thanks...

I am assuming this a heat pump system. From the looks of things you should be able to hook it up using the instructions on page 12 of the installation manual. W2(black) on the old tstat goes to both the Aux and E terminals (jumpered). B on the old tstat likely is the reversing valve and goes to the O/B terminal. Make certain that you configure the thermostat for the correct type of reversing valve. You have to know if it is active in heat or active in cool. If the ducts blow warm air when in cooling mode you got it backwards! No harm done, just shut it down and reprogram the tstat. If it is not a heat pump then the B terminal likely goes to the C terminal on the new tstat.

There is no expressed or implied warranty on the above information, I'm going on what you posted and educated guesses. If the B terminal on the old tstat is common, and you hook it up for a heat pump, you could blow out your new tstat, your system control board, or your low voltage supply. Or a combination of the above. Or the system will not work at all. If you can read the schematics to your system you can figure it all out, but sometimes they can be VERY cryptic. I will close with the refrain; call a professional if in doubt or if you can't afford to repair a mistake.