the first thing I would do is look for a blown fuse. The HVAC module is powered up by fuse #17 in the instrument panel fuse block in the lower left side of the dash. Should be a 10 amp fuse.
here is a picture of where the fuse #17 should be. By the book anyways. Sometimes the book is not correct.
If the fuse is good and has power with the ignition key in the run position, then you have to remove the hvac controls and check the powers and grounds. If all the powers and grounds are good you will probably have to replace the hvac control module.
Have the vehicle scanned. They should be able to scan the hvac module. I'm thinking that there won't be any communication with that module because if nothing lights up or turns on there probably won't be any computer communication. Scanning for all codes may turn up a clue before the module went completely out. It's an easy check.