My HVAC temperature control is stuck on max heat. The knob turns and it is not stripped out or cracked, but the heat stays on max. Before I tear my dash apart I just wanted to check to see if there was anything easier to get at to fix it. Is this a thermostat issue or might this be associated with the oil in the vacuum lines issues I've read about here? I think I have that problem too as my control of the air direction flapper is gone.