98 Low Defrost flow

[tigerscott]

I have a new-to-me 98 V70 no-turbo 320,000Km that I am trying to put on the road.

On of the items identified on my safety inspection is increasing the air flow to the defroster. Hot air does exit the defroster vent when the ECU (not manual) is set on defrost and the fan does ramp up to loud noise when slid to the right. When the ECU is set to the floor or to the vents there is, what I believe is a strong flow, but when set to defrost it does not seem as strong. This could be qualitative observation as the defrost vent is long and narrow and would not feel the same as the floor vent. I noticed that with the mixing valve open I still feel some air exiting the dash vents when the ECU is set to defrost. This may have confused the inspector who did point out that some air was "leaking" out the dash vent and maybe that is where the defrost air was going. At the time I did not know there was a mixing valve.

I have removed the cabin filter (which was dirty) but I don't think that improved the flow.

I pulled the blower and looked in the ducting at the exchanger (A/C or Heater I don't know) and could not see any obstructions.

I checked the motors and they all (3) move the shafts (no broken ends). They seem to have choreographed motion that I can not completely decipher.

I split the passenger side box and watched the floor and dash vent (at least I think that is what the upper flap does) move and seat completely. I cannot easily get to the front motor flap.

I have blasted air down the defrost vent to dislodge any debris but I can not figure out to get anything big, like a pencil, out. I will borrow a flexible scope from work and see if it can find an obstruction next week.

I am resisting removing the dash as I have not found anything that makes me think I will find something wrong.

I am thinking I will submit a clogged filter as the cause and see if it will pass the safety this time. But so much is apart now, and it will sit that way for while while I wait for other failed parts to arrive, it would be unfortunate if I missed something and had to tear it all apart again.

Does anyone have a suggestion what might be causing low defrost vent flow or confirm that there just is not a lot of flow out that vent?

Thanks

[BEJinFbk]

First place that I would look is at the plastic damper flap shaft where it connects to the damper motor.
Sometimes the plastic cracks and can be repaired. You should be able to reach it from the glove box cavity.

This image is from an 850 writeup, but the servo motor locations are the same through '00: