Connecting the unit to the can bus should be relatively simple, the physical side isn't the issue. The problem is that all Canbus systems are not equal. Although the connections and fault codes have not been standardised, the rest of the communication languages still vary greatly between manufacturers.
So what i'm basically saying is the your Avic will need the software to be able to decode any messages from the CAN, seeing as they currently only support ford/VAG i doubt this will be possible at the moment.
I have a full STAR machine myself (identical diagnostic laptop/multiplexer/software as main dealer). When I connect my 2003 CLK I can control/accuate almost every component from the laptop without getting in the car. One thing i can't control is the heater system. (mine doesn't have climate though!)
This is different when i connect either of my parents cars on (2009 R320cdi / 2008 E63) both of these climate systems can be controlled via the STAR.
On cars this age that display climate data via the COMAND from the factory, they don't actually communicate over CAN, but over MOST which is a fibre optic network. Many older vehicles also use MOST to communicate with cd changer, telephone, optional BOSE / HK upgrades etc.
Your user name seems familiar, are you on Mbclub.co.uk. Here's my AVIC install : http://www.mbclub.co.uk/forums/electronics/69071-clk-w209-stereo-upgrade.html