I haven't driven this car for about 6 weeks . The last time I drove it, I used the AC a little just to lubricate the compressor . The climate control seemed to be working normally at that time . Today, I drove it around and moved the temp knob to full heat . None of the fan buttons would turn on the fan . Nothing happened when I moved the knob to full AC ether . The fuses seem to be OK . Where do I start on troubleshooting this problem ? - Thanks

( 1990 300d W124 2.5)

There is a little black box on the driver's side fender with a single "strip fuse" for the heater blower, start there.

If all fuses including this are fine, the next step is to check the blower by measuring and applying power at the blower speed controller connections which I believe are to the passenger side of the blower box adjacent the battery area. There is a fairly recent thread on this procedure and how to test the blower regulator input/output from this same area/point in this forum.

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Gone to the dark side

- Jeff

Yea, my '91 did the same thing, and the strip fuse was gone. Easy to check, just eyeball it, and then see if you are getting voltage to, and thru it when the system is on. If you are, then trace it to the fan motor controller. It's solid state, and expensive, so hope it's not that. If no voltage to the input side of the strip fuse, then the climate control unit is bad.
The strip fuses s just a thin little strip of metal, that costs about $5 at the dealer!

DG

I had the same issue too. Went to the MB dealer, and they didn't have it. However, the local VW dealer did have it. $5.

It was a little tricky to locate. It's a little black box with a flip up top, located near the main fuse box.


Good luck

-tp

That was it . Actually the fuse was OK but apparently connective were weak . I cleaned them reinstalled and use a little the electricians stuff Aluminox ? aka "duck's butter " . - Thanks

Ok, now that the original poster's problem was solved, I have a question to add to this.
I'm having had a similar problem: what would cause only Max or Defrost to not work?

I replaced the strip fuse in my SEC, but it doesn't seem to have made any difference.
The fan still works in auto, and in any of the selected modes other than Defrost.

Thanks for any ideas!

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...