I am losing the ground. This, I am told is the "switched" part of the circuit. I have temporarily jury-rigged this by jumpering the ground pin on the valve directly to the battery ground.
It works this way - prevents hot coolant flow - but whenever the system decides to go screwy again the aux pump runs. I gather the valve and pump work inversely to each other. One is on while the other is off.
Also, when the system goes screwy, the automatic cabin fan regulation is lost. Just stays on high and freezes you out of the car.
Now that I have lived with the problem for a while, it seems to me to be a factor of time... After about 15-20 minutes of operation, the screwiness happens. All is fine for the first 15-20 minutes of every day. After the system is allowed to rest (cool??) we are fine for another 15-20 minutes. Something electronic must be "overheating" and quitting, don't you think.
The good 12V on the heat valve with the rigged, good ground leads me to conclude that the valve is good.
Could this be a faulty temperature probe up by the sunroof switch? or the control unit itself? How can this theory be tested?