I have the same problem on my 95 S320. Except I get no air whatsoever to my footweels. I have been trying to figure it out, but I haven't been able to yet. I have pulled out the glove compartment box, and had a look at the vacuum distribution block. I haven't tested it yet, but I can hear the vacuum going through it. It makes a sound like an air valve being opened, then a sucking sound, then a kind of a click. I checked the codes, it was a relay that was supposedly wrong. So I pulled the relay, then I cleared the codes and ran it for 600 miles. No heat the the footwells, and no new codes. It's about -20-30C here. So, you can freeze your feet really quickly here in that weather even with the heat that is working on max and the vents pointed downwards.
Any ideas how to check, and how to remove the vaccum lines?? What else is there to check?? Where and how to get at it??

__________________
All it takes for evil to prevail is for good men to stand by and do nothing.

Too many people tip toe through life, never attempting or doing anything great, hoping to make it safely to death... Bob Proctor

'95 S320 LWB
'87 300SDL
'04 E500 wagon 4matic