I had this problem for over five months where the fuse (#9) was blowing intermittently. Yesterday i decided to open the heater valve assembly (thanks to bentley) and lo, behold, the auxillary pump was blown. The insulation on the rear of the pump had melted and it smelt like burnt rubber. I got a new aux pump from the dealer ($145) and after 1 hour of labor and 1 new screw clamp, it was back in place. Took it for a test drive and feels good to have not only the heat and AC but also an occasional honk at the jerk who cut me from the right lane.