The ACC PB unit PC board in my '84 300D has been Strip-Eeze stripped and resoldered, but the car still would provide heat only until the car warmed up and then the heat would disappear and could only regain heat by turning the ACC PB unit thumbwheel past the click stop to Max (Note: The monovalve was replaced even though it wasn't necessary . . . no effect. I've also replaced the foam hose up behind the glovebox, and there's a new in-dash temp sensor) and the aux H2O pump is working. I then stripped and resoldered the ACC amp (up behind the glove box) and now it appears that I've got Max heat at any temp setting of the ACC PB unit thumbwheel including when the EC button is depressed on the ACC PB unit. If I turn the ACC PB unit thumbwheel past the click stop to Min, the heat will disappear but this takes 2-3 min. to occur. Anyone got any clues? TIA.

Replace the CCU with a rebuilt unit and a guarantee..........