A/C vent controls

I have a 97 GTP with 143 K miles on it. Just realised last week that the compressor was shot and i am getting it replaced.
Also realised that the A/C vent controls are stuck in one position. Right now if I move the knob, it doesnt do anything and most of the air comes out from the floor vents.
I told the mechanic who checked my compressor and he told me that the changed the vacuum lines but that didnt work.
Can anybody suggest and reasons for this and ways to fix it.
Thanks in advance.

Did the mechanic check to see if vacuum is correct and/or present at least where it goes into the firewall and vacuum distribution block by the HVAC assembly. Lines can be replaced but if there is no vacuum felt at the end of the line you could have a similar problem.

:iagree:

Look under and close to the battery for a small T connection close to the bottom of the front fan. My hose was grey the battery acid caused the hose to break and has no defrost or floor air from the control switch.