Yee-Hawww! Just got my '93 300D 2.5 Turbo! Had a few questions, wondering if anyone would be kind enough to point me in the right direction. First, the aux fans are not coming on. Fuse in fuse box is good. Multimeter battery is out, so I haven't been able to test the resistor in the front driver's side engine compartment. Heard that there are 2 fused relays in the screw down section of the fuse box, haven't checked them yet (just got home and it's dark!) After checking fuses and resistor, assuming they're good, I guess the next thing to do would be to check for voltage at the fans themselves once it's warm. Is there anyway to force fans on, like by unplugging or shorting the coolant temp sensor? I also heard that if the AC is not fully charged with R134, this could prevent the fans from coming on, I guess because the pressure in the system would not get high enough. Also, did the '93 300D come originally with R134 or Freon?

Secondly, noticed cruise control did not come on at all. Is there a way to diagnose whether the switch or the amplifier or the actuator is the problem? I need to get a service manual, but I just got home with my new baby and wondered if anyone could help me with these 2 issues? Thanks to all, this forum is awesome!

Phil

 

You should be able to unplug the aux fans and add direct juice from the bat to determine. The temp sensor (the one with 2 plugs) may not work as these are known to fail. I believe you may be right that there is also an A/C pressure sensor. You may be able to bridge that and by-pass it, and I'm not sure when, or what year the big change happened for R-134. Perhaps this link can help you http://mb.braingears.com/

 

Thanks for the thoughts. Is the connector for the aux fans near the AC receiver-dryer(?-- the thing with the sight glass on it--) in the drivers side front engine compartment? If so, should I be able to unplug it and provide 12 v to either side of the plug and have the fan come on? I assume one side of the plug is for one fan and the other for the other fan. If so, NOTHING HAPPENS... i guess this means I need 2 new fans? ARRUGHHH!
Phil

 

Ok, I feel foolish... thought the fans were connected to ground and each prong of the plug carried +12V, each to a separate fan. Found a picture of the harness and realize both fans are connected together and one prong of the plug is positive and the other negative. Will try this tomorrow before getting a new pair of fans...
Thanks.

 

Mercedes at some years had unique design, that radiator fans have been activated by AC sensor.
When you unplug the connector from AC ACCUMULATOR (the thing with the sight glass on it--) and jump it, the fans suppose to come in.
Again, this is assuming that you have that design.
For job like that it is good idea to get wiring diagram.