I just recently had my last thermostat go bad and am replacing it with a Honeywell RTH7400. It will be running a Carrier Tech2000 Heat pump/AC unit. When disconnecting the wires, I forgot to note which between the white, blue, and brown wires went with what letter. I have the wiring currently set up as follows basing on what I could get from the installation manual and reading others various forum postings:

Red currently connected to R
Yellow connected to Y
Green connected to G
The orange connected to O
The blue connected to C
White connected to AUX
Brown connected to E.

There is a black wire not in use on the last one and was taped.

However, I am not sure on the connections of the blue, brown, and white wires and if the black should still be not being used. Also, when turning the Cool on, hot air is now coming out instead of cool. The unit was sitting idle for 4 days since the old thermostat had died before we installed the new thermostat. Not sure if that has any effect on the hot air.

Can anyone help about if the wiring is rigt and if there is anything in this info that could be causing the air to not be cold?

All you can do if follow the wires to where they land in the equipment and make sure they are in the correct place.

Follow the manufactures instructions that came with the thermostat.

OK, I have checked all of the wiring and have them all correct now matching the unit underneath the house. All were right but the blue and brown (blue is now on E, brown is on C).

However, when the thermostat is placed on cool (set for 73 degrees), it is still blowing hot air when it turns on (temp in the house is now at 85 degrees due to the lack of air conditioning)... hot air also referring that it is hotter than the temperature in the house, as if heat was on. Any ideas why it might be doing that though all wiring does now match? Also, I noticed that the pipe leading out of the outside Carrier unit going under the house to the large box is also getting extremely hot, basically where it'd burn you to touch it. Is it supposed to be that way?

You have to program the thermostat or it will not work correctly.
Read below.


http://customer.honeywell.com/techlit/pdf/PackedLit/69-1900EF.pdf

You have to program the thermostat or it will not work correctly.
Read below.


http://customer.honeywell.com/techlit/pdf/PackedLit/69-1900EF.pdf


It's been programmed fully the whole time. Any other ideas? Needing more specific HVAC troubleshooting.

Thermostat is wired to match the lettering/color of the connections inside the under-the-house box unit, thermostat programmed on all days to 73 degrees during the day 70 at night, outside heat pump unit and fan under the house turn on and blow air into the house, but it's hotter than the 85 degree temp the house is at now (though does say "Cool On" and the system is set on the thermostat as cool). It's reacting as if the heating coils are turning on during what should be cooling... outside temp is only in the low 70's, so it pulling just outside air would be cooler than the house temp, not hotter. Not sure if all that might help.

Check the programing for the reversing valve in the heat pump on the thermostat. That is why I gave you the link. If it is set up wrong it will heat in the cool setting because of the reversing valve is set to reverse instead of being open.
Page 19 heat pump change over valve. Reverse the setting you have now and see if it works.

Ah, thank you for that help. Didn't get all the way to that part, but that definitely explains the issue. Seems it was originally set for a gas heating system by default, so this should solve the problem. Regretfully, the thermostat was missing the installation manual upon buying it, so didn't have that info, and when looking at your link, I didn't go that far down. Thank you so much for the help.

Everyone here is always glad to help.