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Originally Posted by 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
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I can't testify as to how the 300D should work, but I can tell you that you should be able to her the vents open/close if the system is working, although you will have to listen very closely. On the 560Sl, when the engine is not running, the cowl vents are normally closed. When the car is running, and the climate control system is on, the default is for vacuum to be applied to the cowl vent flaps, opening up for introduction of fresh air. When the recirc switch is turned on, the vacuum is bled off of the pods, and the flaps close under spring pressure, therefore closing off most of the outside air from entering the car thru the cowl vents. According to my manual, even when the cowl vents are closed (the system running in recirc mode), only 80% of the air is recirculated, with 20% still introduced thru the vents...ideally. Since spring pressure closes the vents, a leak or other failure in the recirc circuit results in the cowl vents being closed all the time (full-time recirculation). On a 560, you can remove the glovebox and see this in action very easily... Perhaps a 300 is similar. I imagine it so, but cannot say for sure.