hvac system is messed up crazy

hey all. i have been reading old posts for a while about hvac in our beloved e38's. found some info on them but not quite the same problem i have been having. could use some input on how to fix.

it is very odd but somehow when the auto, feet, or the defrost is selected heat is all that comes out. only place A/C is available is vents.

i am leaning towards a complete hvac system replacement. any input on this problem would be much appreciated.

hvac system is messed up crazy