Assuming you looked at http://pages.prodigy.net/jforgione/MB_AAC.html

you can run a flap test
http://www.continentalimports.com/ser_ic40142.html
for the older push button systems it's hold in the REST and 0C/OF button for > 5 seconds.
The chart (chart2) at continentalimports at doesn't quite match the older cars. However step 12 is left footwell long stroke (closed/open leak air) 13 is left footwell leak air, open, 14 is right footwell closed/open leak air, 15 is right footwell open leak air, open

so there are three settings closed, leak air (short stroke), open (long stroke)