obstruction found in air duct behind cabin filter W124
 

The new E220 1994 had weak air flow through the fans, foggy windows
One side seemed weaker.
After worrying and googling etc, I suddenly went mad and started unscrewing
bits from "under there"... the final frontier ... between the engine bay and
the dash
Everything came out fine, I located the filters, which were filthy...
chucked em away
Not bad air flow
Started putting bits back in.
I can not explain why... maybe curiosity.. Pulled the bits out and I stuck
my hand down the guts as far as it could go, only to find and pull out a
filthy old oily rag paper (unknown substance) the size of a hankie.
AMAZING airflow
it hurts my eyes on 4
VINDICATED!!!
Will get some new filters next week

The W210 cabin filters are a piece of cake compared to the late W124s, because the 124s were added on in the middle of the model run while the 210s had them designed in from the start.

The 210 also has a charcoal filter for removing odors. It does work but the aftermarket filters are nowhere near as good as the factory filter. I replaced the factory filter (it was the original and almost 15 years old) but my wife complained, said the new one didn't work as well so I put the old one back. End of complaints. Returned the aftermarket filter and got my money back (it was a "good" German name-brand, just didn't have very much charcoal in it, you could tell by the light weight compared to the factory original). This is one case where the factory part is definitely better.

Jeremy

I wish I could retrofit the W210 charcoal filter into my W124. :(

Changing the cabin filter in a W124 entails removing the whole wiper assembly, since as Jeremy said they were retrofitted after the cabin intake system was designed.