A/C Blows cold and warm
 

2005 A8 on a hot day here in So Cal, my A/C will blow cold air on the passanger side and blow outside air on the driver side. Then after about 20 minutes of driving, the driver side starts to cool to the same temp as the passenger side. Could this be a malfunction in the HVAC blower motor since only half of the car is cooling ?

Not a blower issue; something in heating circuit
 

Per a recent post w/ pic's blower is actually a single unit tied together on both sides. Sounds like your issue is probably with the heating circuit on the driver's side--control valve, switching, etc.--where it is letting hot water through at the wrong time. The water to each side is regulated separately. Others on the board should have more experience/familiarity diagnosing.

unrelated question, what brand of spark plugs do you use? Are the NKG's any good?

NGK's
 

NGK's are factory spec and original install on many Audis, including my W12. Bosch is typically the other. I also found NGK as the original install on my 2000 C5 A6 4.2. Always good luck with them back through many generations of Audi's now. Either supplier is likely top notch with current OE designs, and again know that they are commonly used by Audi in new vehicles. In any case, do buy plugs by the specific fitment for vehicle, not the generic ones also sold; generic Bosch's at many retail parts counters for example won't be the same as the OE spec ones.

ok, thanks for the input. I always by my parts from Genuineaudiparts.com They seem to be the best price and always have the correct fitment/part

I have the same problem with my A8 D3 2005 year.
any solutions found?

Slightly low refrigerant will also do that as well. Always the first step in A/C diag is to make sure you have proper refrigerant levels.

No. Refrigerant is OK.
Hot air blows randomly between two climate zones.
Sometimes both sides.

Need a vcds scan to see what's going on. Otherwise it's just a guessing game.

I have tried VCDS but in vain.
It doesn't show any error codes.