City Rat

Ok, I have had the car approx two weeks now and finally have the electronic version of the owners manual and I think that I have the heat and AC control settings down. That said the possibility of operator error can never be fully discounted. It is winter here and at start up I turn on the defroster. As indicated in the manual the defroster runs high and hard. I turn it off once the windshield clears. The good news is that the defroster is strong enough to heat the entire car so when I kill the defroster I leave everything off and the car keeps the heat for quite a while. HOWEVER, once I get onto the highway and am running at speed, the heat pours out of the defroster vents at the base of the windshield EVEN THOUGH I HAVE NOT TURNED THE DEFROSTER ON. That is all controls are in the off position, no buttons lit and heat blasting me in the face like a hot desert wind at high noon. I thought that it might be the Rest function drawing heat off the engine but when I hit that button it does not light and otherwise does not seem to do anything. I get that this could be a symptom of the problem that I just do not know enough to recognize. I have the Star classic service manual library on CD for the car as I like to pull up schematics and blow up diagrams of each system as a way for me to learn and understand the vehicle. That said I have yet to find a thereblown up diagram of the heating and AC system. Again could easily be operator error

What could this be? Bad thermostat? Some plugged up vaccum lines, stuck flaps in the HVAC system? I just took the car in for overdue B service and was feeling pretty good about things. The car drives nicely, looks and sounds great. This is the only real problem and it is in fact a problem as I just took a 400+ mile round trip road trip. The only way that I could regulate the temperature and keep it tolerable was to partially roll down the rear windows in the dead of winter. Needless to say the GF is in a constant complaining about this though she loves the car enough that she is currently going with the window roll down solution pending a better fix.

Any ideas? What am I doing wrong? I am sweltering in snow storms here! Thanks.

City Rat

Just for the sake of history and completeness cause it is not like any of you guys responded with bright ideas to help out, just saying, lol I thought that I would share the cause of the problem in the event that another guy has this happen to him at least he will have a starting point. Folks on other forums gave me some alternatives from failure of vacuum lines to stuck flaps. All good ideas but in the end it turns out that the MBZ dealership found that it was err, a wiring problem. Well that is to say that it wasnt the wires that was the problem but the MICE that took up residence, at some point in the past, under the fuse box under the hood and chowed down on the insulation of a couple of the wires, specifically the one that gives juice to the defroster. Take a look.