It's going to be hot all week and I need to find out what's wrong with the AC blower fan on my 91 300D. Last week we replaced the aux. fans, then the vacuum hose blew off the transmission line. We hooked it back up and now the blower fan won't work... at all??? no fan heat or cool. We checked the fuses, and all seem ok. We are not sure what to do next! My friend is a mechanical genius but doesn't know much about the mercedes diesel. I need some suggestions and he'll give it a go. Any ideas on where we should look first?? I'd really appreciate the help.

Does the compressor still engage? Also, stupid question but did you check the 30A fuse in the separate fuse holder near the driver's side front shock mount (it is not in the main fuse box)? Even though it is blown it may not look it---you need try to lift it at the center to see if it is still in one piece. Mine blew the other day. I immediately thought the worst but it was the fuse. Mark

all fuses appear good and we read some other threads and found the fuse you mentioned. when we disconnected the fan and put power to it, it ran just fine. Now I guess we have to assume it is the climate control panel?
Can we check that or do we have to just order a new one and see if that fixes the problem?
Thanks for the advice... it's nice to have someone to talk to about this, I know so very little...Deb

Not necessarily. Check out this link http://www.peachparts.com/Wikka/W140BlowerMotor (different car but same principles) to help determine if it is the pushbutton control or the blower regulator. Mark
PS. Dang---it only took me 3 edits to get the link inserted properly.

Yes, the compressor comes on. The pictures you sent were excellent. My car does not have the same filters and the panel looks different but the parts in the motor should be the same. We are going to take a closer look tonight....
Thank you, again. I have located a rebuilt control panel that has a warranty if I need to replace it and it is priced reasonably. Slow and steady wins the race. Deb

Do the diagnostics in the article. My bet is on the blower regulator although if the push button control is original it could be that. Also, carefully (don't tear the fuse in two) loosen and retighten the screws on the fuse or remove the fuse, screws, etc. and clean with scotch brite (r). Galvanic action between the aluminum fuse, brass fuse box and steel screws can cause problems. Mark

Your 124 chassis is a bit different.
Three easy diagnostic test.

Turn key on and fan control on defrost. Jumper a wire from bat positive to each side of the fuse.. if fan then runs , fuse connection is bad.

At firewall behind brake booster, three prong plug [ Red/Blk/Yellow].. with volt meter , check for power at yellow wire .. this is power from control panel and it is a variable voltage [ depending on fan speed selection] of 2-8 volts. This is the trigger signal for the regulator at the motor. If no power here , CP/circuit is suspect.

If trigger voltage test is verified to have voltage, then At fan motor, run a jumper wire from the blue wire at fan motor to ground .. if fan runs, regulator is bad.. This test eliminates/bypasses the regulator and regulator trigger circuits.
Remember , the fan always has power at the red wire ..it is the blue wire
[ neg side of circuit ] that does the fan switching [ called a 'Switched Ground" circuit ]. That is all the Regulator circuit does .. it controls the Ground side of the fan motor...

Way to go guys!!! We did it!!!! We took your advice, started with the early suggestions and by the time we cleaned the fuse and its connection we were in business again. I'm so happy!!! So glad I didn't order the control panel. You guys saved me some big bucks!!! Thanks again, gotta love my cool little diesel
Deb

Did the fan stop working when the trans vac hose was reconnected? Sounds like one is related to the other.

If it's not related, could be the fan or regulator. If you get another fan, new or used, you can hook it up easily to a different regulator to see if your existing fan works (once you get your existing fan out).

Good luck, and if you need repair instructions, contact that wizard, jbach36.

1991 300d, 90k