First check for any fuses under the hood or inside that blew from the surge when reconnecting the new battery. If they're all okay, you got caught by one of GM's many tricks to get you to go back to the dealer. With newer vehicles you must never disconnect the battery. Use some type of memory saver to keep all the many computers' memory circuits alive. A heating control system failure is not one of the ways these vehicles normally act so I'm hoping you find a blown fuse, but if not, the dealer will have to unlock or reprogram that computer.