If the air flow is good and strong, but the temp is not, could be a restricted heater core.
If the heat at the top is good, but cold at the bottom, then there is a flap / motor issue.
Using a scan tool, "basic settings" can be initiated to run the system through its open closed cycles.
Fault codes are present when you turn the Climatronic ON and the display flashes for a while.
Sample of restricted / bad heater core from a Jetta:
http://www.youtube.com/watch?v=kQhV49nExaw
Thomas
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Friday, December 28th, 2012 AT 2:09 AM