Most times I have seen either a bad switch or broken vacum lines. you might want to make sure that none of the line got mixed up if they were removed at some time.
The HVAC system is under computer control on the RAM and when the system detects a fault, it will shut the control motors down until the next calibration cycle. It will continue to fail and go...
You must remove the dash, at least partially.
undo the steering column and alow it to drop onto the seat.
remove the centre console, and all the small bolts/screws along the top of the dash. There...