XC90 v8 all wheel drive defroster issues

[WestCoastBilly]

So I get almost nothing out of the defroster, but the main vents and floor vents work fine When switching between floor and main vents. Switching to defroster, air blows out main vent.
Any help would be great.

[ggleavitt]

Might be a damper not moving sufficiently, no easy way to test in my opinion other than with a connection to the vehicle using a DICE unit and VIDA or another tool that can perform Volvo CCM testing and calibration. Entirely possible you'll have a code for this if you were to do a scan.

This vehicle have heated seats and are both sides working properly? Might be a long shot but see below for what functions stop working when a bad SHM kills the LIN bus.

Left hand drive vehicle:

The following components communicate on LIN bus 1 (Driver Side):
Damper motor module (DMM) for air distribution
Damper motor module (DMM) for temperature left
Left-hand seat heater.

The following components communicate on LIN bus 2 (Passenger Side):
Damper motor module (DMM) for the defroster (ECC only)
Damper motor module (DMM) for temperature right
Damper motor module (DMM) for recirculation
Air quality sensor (AQS)
Right-hand seat heater.