Does the recirculate air option really do anything?

[jbach36]

I have the circular arrow button that is supposed to recirculate the air. From memory, the manual says don't use it for more than 20 minutes, or maybe it shuts off after 20 minutes. It's supposed to be when you're coming up into a dusty area or where they're doing road work, so you don't get the dust inside the car while using the blower fan.

On a Jap car, when you do that, you can hear the air panels opening or closing, it helps the a/c cool down quicker, you can keep it on all the time, and when you put it in the recirculate mode, you can really hear and feel the fan increase. On my MB ... I don't hear or see any difference. No increased fan sound. No blower fan panels moving to open or block off air from the outside. Just ... nothing.

So, I have to ask, does this mode actually do anything on a MB?

1991 300d, 90k