Volvo: front defrost, scan tool, vst

Question
When defrost is selected to clear front window, very little air comes up through vents, even with fan on high.  Heater works fine, as do the other vents.  thank you

Answer
Amanda,
Some older model Volvos use vacuum to open and close the vents. If your car is using vacuum check the hoses that supply the vacuum to the dash. On newer Volvos the vents use small electric motors to operate the vents, in that case they maybe loosing a signal and or need to be calibrated. That is done with the VST Volvo scan tool. I also have seen some models that the heater control head is defective and needs replacement.