First I've heard it called that, but it's usually called the heater valve motor. It's a gearbox motor that opens and closed a valve that controls the hot water flowing through the heater block.
Mine did malfunction and it really sucks having to drive in the winter without heat! Impossible if there is snowfall.
But I did manage to fix it myself, including fixing the actual motor... well... at least it works for now, but for how long I don't know.
Look at my blog if you want to know how I fixed it:
http://www.mitsubishi-forums.com/t28510-no-heat.htm