Cam anybody suggest how I could find out for sure wether my air recirculation works. When I use my AC in my 88 300E and I press the air recirculation button, the red light on the button comes on, but other than that I can not tell any difference. When there is something "smelly" outside such as a stingy exhaust from another car, it quickly gets in my car even with the air recirculation on. There are no leaks from anywhere else in the vehicle, door seals and such are all fine. Thanks for any help.

Simple!
 

Find the recirculation in-take in the cabin. For my C-class and for a W140, it's under the passenger side dash board.

Once located, turn on air recirculation, and then put a peice of paper/tissue or some smoke and see if it sucks when on recirculation, if it isn't, then you know.

I hope this made sense. Good luck!

Follow David's advic, on the W124 in the same location, behind the glove box. Hitr the button. If it is working you should noticew an almost immediate change in the sound of the air flow. b If this isn't happening, best bet is your vacuum actuator has stopped functioning.

Or you can try this....
 

Get behind another vehicle (preferably one emmitting lots of smoke and fumes) with the recirc. "on." If you can smell the fumes, it's not working.

No two ways about it.

(And if it isn't, don't forget to get away from behind that car immediately!!!)

By the way, air recirculation won't work if you engage the A/C economy mode (that's if your vehicle has that feature).

Good luck!

Where the hell did I learn to type. :)

Thanks people. I have trouble locating the air recirculation intake though. When you say behind the glove box do you mean that i have to remove the glove box to see it? Because I can not find any air intake under the glovebox. I can only see the two lower air outlets on each side of the main tunnel, but no air recirculation intake.