The car is a 1986 420 SEL.

I unplugged the connection and with the engin running, checked the voltage in the plug. Receiving full voltage if interior temp control is full cold or full hot. I didn't allow car to warm up fully, so maybe there is some control that gives full power until engine is operating temp.

My only guess is that there is a broken wire in the coil that goes around the magnetic monovalve plunger. Any thoughts on a way to check this?

Brian