The previous guys who wrote are right that you do not need to remove the cowl below the windshield. However, I recommed that you do remove it because you can remove and replace the cabin air filter easier, and, just as important, you can clean the air duct that leads to the ventilation fan.

1. Take off the wiper blades and unbolt several screws that hold down a black panel at the base of your windshield.
2. Remove the old cabin air filter (on the right side of a USA S70)
3. Look down the duct below. I have seen several S70s that were really nasty because the owners had never replaced the filter (they never read their owners' manual?) Clean all the sludge, leaves, and mold you will find down in there. Use a strong cleaner like Simple Green or 409 to scrub everything you can reach. On the V70, you can reach the fan blades and clean them one by one. Be methodical.
4. Spray Lysol or another antibacterial agent or Wurth AC spray down the tube while the AC is running at high speed.
5. Reassemble your car.

Note: this is also an opportunity to tighten the screws to your dashboard.

Have fun.