I exchanged a GE thermostat (not sure of the model #) with a Honeywell RTH230B today. Coming from the wall, there is a red, white, yellow, green, and blue wire; however the blue wire was not connected to the old thermostat. I'm 100% sure about this, it was capped off and wrapped around the other wires.

After connecting the wires to the new thermostat R-Rh-jumped-to-Rc, W-W, Y-Y and G-G, no cold air comes from the vents in the house. The outside unit is running, but the air coming from the vents is 79 degrees, measured by an independent thermometer.

I removed the new thermostat, put the old one back on, and still no cold air. Have I broken my AC unit?

Hmm... did you shut off the power to the furnace BEFORE you started the installation?
... and did you happen to notice if the wires were actually connected to terminals they are supposed to be connected to on the old stat before you disconnected them? Since you can't get it to work again, you may have shorted some component, or perhaps the wires just were not wired to the actual code in the first place. What type of furnace is this, gas, electric?

Power was off during both new installation and old re-installation and the original wires were hooked up correctly to their corresponding labels on the old thermostat. The thought that I'd blown some fuse or shorted something had crossed my mind, but I have no idea how to check for this. It seems strange that the outside unit is running and I see condensation on the piping running inside to the unit, yet the air coming from the vents is ambient-temp.

It's a gas furnace and an electric (are there other types?) AC unit. The heat is working. Any further help would be greatly appreciated.

Can you check to see if perhaps the burners are firing at the same time the stat is calling for cool? Is the fan running at the same speed as before you changed the thermostat? IS the fan running? There is always a chance of a broken wire when changing a thermostat.. is that a possibility?

The fan is running, but I don't know if it's going at the same speed as before. It's easy to convince myself that the air is coming out slower/more weakly, but that's probably just my imagination.

I'm already late for work this morning, but I'll take a look at the heat/air running at the same time suggestion when I get home this evening (to my hot, hot house). Thanks for all your help.

Well I went home yesterday at lunch to see what I could see and strangely, the AC was working. I assume there's a wire somewhere that got jiggled loose when I was working on it Sunday and just happened to fall back into contact sometime. Guess I'll need to hunt it out before I lose AC again...

In a possibly un-related question, how long should it take for a 2-ton unit to cool a 900 sq. ft home from 83 to 76? It took a good 3 hours for it to happen yesterday, which seems excessive and I'm wondering if I should get it serviced.

Thanks for your help.

Depends on a lot of factors, insulation, outside temperature, shade trees, windows. That being said, stick a thermometer on the supply register closest to the furnace / hvac unit. The air needs to be cool for the unit to do it's job. It's not a sceintific measurement, but my supply air is now at 53 degrees and the house is at 73. Can you go outside to the condensing unit and see if the suction line (bigger line) is cold and sweating? This is often a way to indicate the charge of refrigerant. If an air conditioner cycles normaly after cooling the house, it's probably not too big of a deal to fine tune the system.