weather or not it's plug and play depends entirely on what equipment he connected to the stat, and how it's connected.
Good point. Can't necessarily assume an all-Infinity system. All communicating components will automatically be identified and many parameters set accordingly. The installation menu still contains items/options the installer would have to configure.
UPDATE: called my normal HVAC guy. he pulled the thermostat and we went to carrier parts dealer in town w/ my closing documentation (since the warranty was 5 years which the unit exceeded but they go by your close date luckily). they did the warranty paperwork and out i left with a brand new unit and no money out of pocket.
plugged it into the existing harness and let it do it's equipment detection and checks. i took pics of the old thermostat and settings and i verified that it found the right equipment. verified the settings and everything's good to go.
to answer the post above, the entire system is carrier infinity so it was pretty much plug and play with the old fault codes and serials passed through to the unit.
mine was version 12 and i came out with a version 23. there were a few extra options in the service mode and layout looked a little different but i didn't see anything drastically different.
thanks for the help. saved me some bucks and i got a new thermostat.
i can't believe these things cost as much as a smartphone if i had to pay retail.