ACC T-Shooting Ideas??

[TomJ]

Once again trying to diagnose no low fan voltage in Auto or Low in the 1984 300D.

Have 5 ACC units from 1982-1985 cars, four of which have been re-soldered, those four operate the fan on high, NONE of the units will turn the fan on in "Low" or "Auto".

The blower controller relays click (have four of these and three temp regulators, all have been switched and swapped with the same effect) and I've even opened up one to WATCH the relays open and close depending on ACC settings.

Changed out the temp sensor on the dash with THREE different ones, tube is fine, NOTHING seems to change the fact that the fan gets zero voltage at the Low or Auto settings (get's batt voltage on High fan setting.)

So..., it's NOT the fan (rebuit, D/C'd and voltage to the fan checked), probably not the ACC units as most were out of working cars and have been re-soldered, all work (or do not work?) the same way except one that hasn't been re-soldered, it doesn't do anything. Tried FOUR blower controller boxes, all do the same clicking and none acts differently from another. Three temp regulators, again, all work the same way (maybe all of those are bad?) And three different temp sensor units.

Engine is up to op temp, the engine temp sensors are fine (the one at the thermo is old, not sure about that one), re-built monovalve, operates properly, rebuilt aux coolant pump, operates flawlessly.

Anyone have more ideas than what I could find in the archives of ACC posts I've gone through?