I finally had to get the Mercedes zone rep to look at the air flow on this E420. The dealer had checked it twice and both times delcared the system working normally. The Mercedes rep immediately agreed with me that there was a problem. He had the dealer tear out the instrument panel to check the vents etc. The service invoice indicated that there was a problem with a control rod and they also cleaned and lubed all vent doors and rods. The system now works like it should with great cooling. I think the Mercedes dealers should let their mechanics drive the various models more often so that they have some clue as to how things should be on a Benz!