Volvo VHD - Manual (Page 182)

176 Heating and Air Conditioning
Air Vents
A Closed
B Open
C Lateral Air Flow
D Vertical Air Flow
When heating the cab, all vents should be
closed. However, the vents on the outer
parts of the dash can be used for defrosting
the cab door windows. When operating the
air conditioning, all air vents should be
completely open and the air flow directed
upward.
W8001150