I am having trouble figuring out the wiring for a new programmable thermostat installation.

I am replacing a RobertShaw 9420 thermostat. I bought Honeywell RTH7500D programmable thermostats to replace it because I wanted a programmable thermostat. I have central AC and a heat pump.

The curret thermostat is wired with the following:
Red Wire > R
Yellow Wire > Y2
Green Wire > G
White Wire > W2
Orange Wire > O
Blue Wire > C
There are also a brown wire and a black wire not used coming out of the wall.

The new honeywell has the following connections:

Conventional --- HP
C --- C
G --- G
Y --- Y
W --- O/B
RC (jumped to R) --- RC (jumped to R)
R --- R
W2 --- AUX
Y2 --- E
--- L

Any ideas on what wire goes to what? I can't figure out the orange wire and the blue wire and I don't know if I need the brown or the black.

Thanks!
Paul

How are the wires connected in the air handler/frunace? Post back with that Iand I may be able to help.

I am sure I already answered this, but don't see my answer. As I said, the blue may not be needed, just cap it off.

These W2 --- AUX
Y2 --- E
--- L
Contacts may be for the thermostat to control different rates. Some of them may be for an outside temperature sensor. If the heat pump doesn't have the same labels as the thermostat, you will need to study the installation manuals for both to use the special features.

The only wires that connect to the air handler in the attic are the following:

Red
Green
White
Blue

There is also a brown wire coming from the air handler that is capped off.

The yellow and orange wires seem to come from the AC unit outside.

I contacted Honeywell support and Robertshaw support and they don't seem to understand why the yellow wire would be connected to the Y2 terminal instead of the Y1 terminal in the current Robertshaw 9420 thermostat. Nothing is currently connected to the Y1 terminal. However, I do notice the AC unit outside blowing when called upon.

And thanks, Labman, I noticed you did respond to another posting I did. I should have cancelled that other posting because I think I put it up in the wrong forum and I also had some fact wrong in that one.

Not all systems are set up to use different heating and cooling rates. You may not need the orange and black wires at the thermostat. If the cooling works now, and the heat does when you need it, I would leave things alone. If the heat doesn't work, try the W1 terminal on the thermostat.

And thanks for reassuring me I had responded to the other thread.