I just completed the repair of my defrost vent/register blend door actuator. Here is a quick summary in case it can assist someone else on the site.
PROBLEM: No air circulation from the defrost vents that are on the top fascia/instrument panel near the windscreen/windshield.
FAULT STEPS: Turn on climate control system and moved through all options for both cooling and heating. Move through all vent option positions: floor only, dash only, mixed floor and dash, defrost. All options worked correctly except no defrost ventilation. Selected auto option and rear defrost, then front defrost. Again, all options worked correctly except no defrost air circulation. I reviewed Technical Bulletin JTB00066 titled, Ticking/Bubbling Noise Behind Fascia/Instrument Panel. I have experienced this condition, but it never prevented any functionality of the climate control system.
CONCLUSION: Since all options worked correctly except the defrost air flow I decided to replace the defrost vent/register blend door actuator, part#: XR8 57885
REPAIR: I followed the repair procedure in the Service Manual in section: Electrical > Climate Control > Control Components > Defrost Vent/Register Blend Door Actuator > Removal and Installation. The Instrument Cluster needs to be removed first and that can be found in 413-01 Instrument Cluster, Removal and Installation. The front instrument finish panel comes off easily if you use plastic non-mar removal levers. Just make sure you are close to the clip locations so as not to stress the finish panel and the plastic clip retainers. The instrument panel comes out easily with 4 screws for the cluster finish panel (philips) and then the panel itself with (4) 7mm screws. The 2 electrical connectors on the back of the instrument cluster are the type with a lever that needs to be lifted and moved from top to bottom as they basically act as a lever to release the connector. (When reinstalling they help seat the electrical connector.) The left and right sides are color coded. The actuator is located exactly where the picture says it is; yes, way back there. It can be removed with some careful positioning of hands and tools. It is a tight fit. I removed the 3 actuator screws from the front and the electrical connector from the bottom. When you mount the new actuator be careful to get the pin on the actuator lever into the vent door arm. Also, near where the furthest screw from the front, on the actuator, there is a hole where a pin goes into the actuator, this helps make sure the actuator is properly positioned.
This repair solved my defrost problem and I hope it helps someone.
Here is a picture of the inside of the old actuator. You can follow the broad circuit traces to see where the positive and negative pins are located.