If a 190 starts to circulate an antifreeze smell and steam, the heat exchanger (or heater core if it is called like that) is most probably broken (this is a quiet common problem of the 190 in Europe).
I think mercedes thought that this device would never break down whilst engineering the 190, because you have to take out most of the parts around the dash (including the complete dash) and behind the engine (underneath the windscreen) before you can get to the heater-home & heat exchanger.
I have changed these heat exchangers several times myself now and I must admit that it is not as tough as it appears to be, but you have to now what you're doing (with the proper tools).
To get the heater-home out easily you have to remove the windshield wiper & plastic caps underneath the windshield/behind the engine cause that's the place to find the mutters to unfasten the heater-home.
Inside the car you have to remove steering wheel, console and dash (which can be done within 2 hours) & when you've removed these parts it is not that difficult any more...as long as you know what to do.
Do not start removing the parts before you know exactly what to do!
with a minor 600+k