I have a 94 V12 and this year the AC has started blowing mainly on the floor, rather than the dash vents. It does got from hot to cold as I change the temperature knob, and when I select defrost all the air goes to the windshield.

However, when I select a temp, say 70 and auto, most of the air goes to the floor, no matter if it is heat or cold. Needless to say, it not nice to have refrigerated toes, any ideas where I should start looking?

I have checked the lower servo motor and it functions.

 

Sounds like a possible vacuum problem. You might find this diagram helpful.

 

I hadn't thought of a vacuum line coming off, I'll check that.