Thermostat + Arduino

I have all the equipment I need I just need help understanding how to interface with my thermostat. I want to be able to monitor and change my temperature via my smartphone. I have a "Carrier TSTATCCPQ501" thermostat, it's manual can be found here The board connects to the wall via 7 pins labeled from top to bottom as " C, W, Y, B, O, G, R ". Any help would be greatly appreciated!

C = Common/Ground
W = White wire. Connect to R for Heat
Y = Yellow wire. Connect to R for Cooling.
B = Brown. Set heat pump to Heating mode.
O = Orange. Set heat pump to Cooling mode.
G = Green. Turn on the circulating fan.
R = Red. Provides +24v.

In many cases only W, Y, G, and R are used. If you don't have central air conditioning the Y won't be used.

Thanks for the reply. I have a few more questions I'm still a bit unsure on how to proceed. How would i convert 24VAC to 5v? From my basic understanding Arduino measures voltages compared to it's ground. How would I interpret these voltages from my central air thermostat connection?

A bridge rectifier and filter capacitor can turn the 24V AC to 24V DC. You'd then need something like a voltage regulator or DC-to-DC converter to reduce the voltage to 5V.

I'm not sure what you mean by "interpret these voltages". What did you want to know? Pretty much 0V means (Heat, Cooling, Fan) OFF and 24V AC means ON. These are all outputs from the thermostat to the heating system.

I want to be able to monitor and change my temperature via my smartphone.

I don't think what you want to do will be easy trying to hack the thermostat. The below seems to be nice but $$$. There are other wireless thermostats that are cheaper that might be worth a look. Back in the old days, t-stat remote control was easier.