Could be the oil in your refrigerant getting on the windows. If the evap is leaking, then this could be the case.

My 1995 E420 had an evap leak that went from fully charged to empty in 24 hours. I noticed a very distinct odor while this was happening - chemical-like.

I hope it's not the evap - not a fun or cheap repair.

Troy
1995 E420 98k