It has been many years, but I think that car had a sensor on the engine to keep the heater from blowing untill the engine was warm. I would explore that angle! I had a 85 300TDT. BTW the default on the mono-valve is heat, it is normally open and closed by the heater control module. Dont know about the hose, could it be a drain hose from the vent, the flattend part would indicate that