Auto Parts: Audi Air Conditioner System, bar graph, audi a8l

Question
My 2002 Audi A8L's air conditioning system will not always run.  I'm sure the heater will do the same thing when it gets cold.  It just doesn't come on at all.  The fan speed indicator runs across the screen like it is on, and all indicator lights on the dash will show it on, but nothing happens.  Then, all of a sudden, it will run normally for a while.  It may run the entire trip, or just quit while driving down the highway.  I think the compressor is running the whole time, though I'm not sure.  I can punch any button on the dash, and it has no impact.  The car has 165,000 miles on it but is in great shape.  What could it be?  Almost has to be electrical, I think.

Answer
    If I got this right, the car thinks the system is blowing air on you, but nothing is coming out of the vents.  One of two things has happened: the doors that move to mix the air from the various sources together and send it where you tell it to go are stuck or inoperative, or the blower motor is bad.  Most likely the blower motor.  The climate control computer applies twelve volts to the motor to make it spin.  If the motor doesn't spin, the computer has no way to know.  That bar graph on the controls is telling you how much voltage is being applied to the blower motor, not how fast it is actually spinning.  If you don't hear the motor spinning back there behind the dash, and the controls say that it should be, then it is probably bad.  Even though the car is not all that old, it does have considerable mileage on it, with the motor spinning most of that time.  The motor needs to come out, be bench tested, and probably replaced.  While it is out, someone needs to look inside the airbox where the motor goes and see if any debris has dropped down in there.  That could have caused the motor to go bad, so vacuum that space out properly before replacing the motor.  As to whether you could do this job yourself, I don't know.  If the motor is under the hood, you probably can.  If the motor is inside the car, run away screaming and hire a pro.