I have a 2001 S40 with a whimpy defroster. When in the defrost position, there is a lot of blower noise under the dash, but very little air. It seems like the ducts were never connected at the factory. My Volvo shop says that S40s have whimpy defrosters. It’s sort of hard to believe for a car designed in Sweden.
I’d guess the blend door isn’t working.
If the doors in the HVAC system are operating correctly you should get just as much air from the defroster vents as from any other vents.
I think the air is not being directed fully to the defroster vents.
I agree the air is not being directed to the vents. I’m trying to find out if this is a typical problem. When a Volvo specialist garage says “all S40s have whimpy defrosters,” I get worried that the issue may cost me big money.
This car has acted this way since it was new. The selling dealer claimed “works as designed.” Now that I live in a snowy area, it’s got to be fixed.
I’m wondering how much space is under the dash. Is it possible for a duct to be disconnected? That may not be physically possible.
Here is a cheap solution: purchase a defroster fan. These are available at discount stores in the auto parts section and at auto parts stores. Mount it so that it blows air where you need the vision through the windshield. Most come with a plug that fits into the cigarette lighter. I rigged up two of these for a rear window defroster on my 1978 Oldsmobile. This did the job.