91 300D fan repair
 

Hi all. This is my first post to the forum so go easy on me:)

Hi have a 1991 300D (love the 30+mpg), but the AC fan has not worked properly for over a year. The symptom is that cold air leaks out of the center registers (nice and cold), but the fan speed never goes past low. I have replaced the Climate Control electronics which has the fan switch (low, auto, hi) to no affect. There is no fan noise and no noticeable air flow other than what leaks out.

I do most of the repairs on my vehicles, but I hesitate to tear into this dash without a little guidance, tips, or youtube helps. Any help?

If it were just a problem with door actuator, wouldn't I still hear the fan blower? There doesn't appear to be fan noise at all..

Climate system diagnostics
 

I recently got the repair manual from mercedesmanuals.com and read through the information on climate control. My symptom is no blower operation. I've tested the actuator doors by switching modes (defrost, upper+lower, off) while driving at speed. The ram air seems to be coming out the correct vents depending on the mode. I also get hot or cold air depending on the temperature dial. What I don't get is any fan operation. I've already replaced the climate control unit with the buttons without affect.

Is there some way to diagnose what part needs to be replaced (blower, blower control, sensor)? I read about a procedure 83-503 involving an impulse counter on coupling X92 or X11/4 but could not find the actual procedure document.

Thanks for any help.