if its a fully electronic climate control with seperate buttons for different functions I'd imagine you'd need to get an interface phidget and then one of their relay boards. then replace your buttons with the relay board which allows you to effectively turn them on and off digitally. You'd need a bit of programming experience but it wouldn't be too hard.
If it used the same buttons for multiple things then it would probably be a little harder and I can't say much without more information.
I'm considering trying this on a manual climate control type system with control cables