Maybe that's the reason? Google search for "Mercedes Benz C230 Kompressor obd" brings up few problems with various "dedicated" obd scanner devices and also some information about Mercedes Benz protocol incompatibility with many of them (I think you might have read the same threads on mbworld.org forums)... You could try to debug what's going through the port and check why it hangs.

By the way, I also drive a pretty old car with OBD and had similar problems (pyOBD not connecting or hanging with time), but solved them by increasing the timeout (it pops up during "connection" stage) significantly (to something close to 30 seconds or even longer). (by the way, list on http://www.ebay.com/itm/Scaner-ELM32...-/261766627015 says that ELM327 officially supports only Japanese gasoline C230's... also the website http://www.outilsobdfacile.com/vehic...-obd2/mercedes doesn't list the 1999 C230 as compatible... but maybe these lists are incomplete)