OK. I'm looking at my heater control unit and wondering waht to do. I'm not even sure that this is the source of my trouble, but with the fix described in this thread I can at least get started. The heater works; the AC works. But I can't control which will blow into the passenger when. For the most part, I can't keep the heat from blowing into the cabin. Will installing the valve and bypassing the HCU address this?