HEVAC control unit differences

Anyone know the differences between the various part numbers for the HEVAC control unit? Seems they have been changed at least 3 times over the years, part number JFC102550 being the latest I think, and as fitted to my car. The external temperature display on mine is wrong, seems only to show between 9 to 14 degrees even if warmer than that outside. Changed the temperature sender unit behind the bumper but no difference. I'm not gonna buy a new one from LR at almost £600 just for that silly fault, but one from fleabay may be OK. But would an earlier unit work? I have the book symbol on anyway, but not checked for error codes as my Faultmate is currently setup for my Freelander and I need to purchase the relavant software for the P38 but was putting it off until I get a more major fault. The air con seems to be working fine, hot/cold/up/down from all vents seems fine, and I had it re-gassed recently too.