The defrost pod and door I believe on your car can only be accessed by removing the dash.

Best bet is to check out the online service manual, it has a very detailed description of the operation of the ac system and where all the doors and pods are.

startekinfo.com, click on MB Workshop Resources on the left side, page through until you find Chassis 126 manuals.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech