The W210 has two CAN buses. The body bus and the power train bus. Neither of which can be read from the OBDII port.

The power train control modules (engine and transmission) use ISO 9141 protocol to the OBDII port over a dedicated wire from the ECU.

The way this car does diagnostics is each subsystem has a dedicated wire back to the 38 pin connector in the left side fuse/relay box. This can only be read with the proprietary Mercedes tools (the HHT or Xentry).

To help with the AC diagnostics there are special diagnostic modes that can be accessed by hidden menus in the AC controller. Unfortunately you may not be able to get to these because if the AC controller is locked up it won't let you get to the diagnostic mode.

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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