86-up W126 ACC blower controller
 

I did some checking on the ACC blower controller of the SDL because the fan isn't working right. I didn't get very far but I discovered this much:

The controller sends a constant 12V to the red wire and varies the voltage to the blue wire. Close to ~0V for max and ~11V for min. The controller input is a varied voltage through the white/green wire. ~1.3V for min, ~7.7V for max.

Symptoms:

- fan works properly with key in 1, engine off. I can switch between modes and fan speeds with no problem.

- with the engine running, it's rare that I can get the fan started if it was on max when I started the engine. Spinning the cage doesn't help.

- to use the fan, I have to glow with the fan switch in max. The blower comes on, I start the car and all's well if I leave it in max. If I put it in auto or min, the fan will slow down then stop. Can't get it started again unless I restart the engine.

Seems like one of those things that happens to the other guy.

Blower motor is new, blower controller came with the car. I have the 91 SE as a parts source for further diagnostics. As far as I can tell the controller is sending the right voltage to the motor. I don't know about the current because I only know enough about current to know not to hook up my 10A-limit DVM in series with the motor.

As if that wasn't enough, the SD blower will only start if I set it to DEF or TV in max. Then I can switch out an everything's fine for the rest of the trip.

One ACC problem at a time, please.

Sixto
91 300SE
87 300SDL
83 300SD