I have a 98' V90 and heat blows out the vents unless the car is at idle. When I accelerate heat comes out of the vents even when the temperature control is on the coldest setting. My guess is the heater door is opening when it is not supposed to.
Any ideas on what I should check?

 

I noticed this as well... I wonder if it's a feature that might be disabled?

 

This was common on the old 960 and V90. I believe that the problem sources at a leak in the vacuum reservoir.

 

Wow! Thanks for the timely info. I'll show this to my tech and see if he'll do it...