Hi, I have a similar problem, 2002 MC (Auto AC) the thermostat seems fine, Temperature gauge stays in the middle after about 10 minutes, blower is working, both matrix pipes are red hot, flap is opening, Matrix gets boiling hot but still only warm air comes through. I will flush the system out with some cleaner and replace the antifreeze to see if this works. An old thread covered this same problem and they did everything apart from replacing the matrix and when they fitted a new one it worked properly. I think the fins inside the matrix are so thin that they must get blocked up easily as soon as the fluid gets a bit dirty. I'm going to do this at the weekend so hopefully it will just be warm enough to get me through winter as I will be selling the car very soon!