Date registered: Dec 2005
Vehicle: 222.132 & 221.122 & 213.050 & 906.633
Mentioned: 3 Post(s)
Quoted: 40 Post(s)
5 replies and no feedback from the OP, on the other hand the question was only posted a day ago. Some more details about the issue would be useful anyway.
It may not make a difference but is this a W120 or a W220 model (US)?
The AC leak could lead to reduced cooling but this should not be an issue if the engine is warm and the ambient temperature is lower than the heating temperature setting. But we should know if the issue only happens at start up or also while driving. I sort of thought the "after 20/30 minutes" means it comes back while driving?
Anyway, you should have noticed if there is some refrigerant leak, had the AC system been checked for this?
The "steam up and warm damp smell" sounds more like a heat exchanger leak at the heater core, the antifreeze creates a sweet smell. But eventually you should have noticed some loss of antifreeze from the radiator, is this not the case?
If the smell is like mildew, either your HVAC is otherwise OK but just needs a treatment that kills mildew and bacteria. A heater core drain pipe would make water stay at the HVAC housing and would allow mildew to grow.
Too many different options to speculate about without some additional info about.