92 audi v8 Quattro - windshield defrost air vent
 

When I turn on the Defrost, the air does not come out of the windshield's 3 air vents. It onlys comes out of the front driver and passenger side air vents. I checked the recirculate doors and the spring are okay and it was not clogged. The regular A/C and heat are working okay. Is the cause the A/C Servo malfunctioning and needs to be replaced or is there another part that controls these 3 air vents?

RE: 92 audi v8 Quattro - windshield defrost air vent
 

If the ’92 V8 system is similar to my 1991 100Q then probably the servo is defective. Mine works intermittently and gives me the 07 & 15 error codes suggesting that the problem is with the servo. What I have read is that these servos have a tendency to crack or strip the plastic gear.