On my '84 SD, I've always had fan trouble. Years ago, if run on high too long, it stopped working for a while. Usually ran ok on medium or low. Now, it doesn't run right away. If I drive about a 1/2 hour, it starts running. Any tips to a solution?

Thanks

__________________
1984 MB 300SD Turbo

Search resolder W123/w126 blower control panel, had to do it on two of mine. Or push panel around control after up to temp.

I'm betting the brushes are shot. Before taking a lot of things apart, apply +12V directly to the fan motor. Four screws and drop the passenger knee panel. You don't even need to pull it to test.

Some have extended the life of the blower motor by replacing the brushes. However, when I tried this it was a short-lived fix. Eventually, it called for replacement of the blower motor.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

That Bosch uses (Almost) Hardened Brushes
(Which Would "Cut" into the Rotors "Slip Rings".)

__________________
'84 300SD sold
124.128

Have you checked the fuseholder for signs of poor connection or heat? Failing after running on high speed for a while suggests something is getting hot and opening up from current draw. 1986.5 and later W126's used an external fuse holder with a 30A strip fuse to alleviate issues with the fusebox-based 25A fuse of the earlier models.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I tested fan, and it runs great. Since the A/C worked ( just no blower ) I kept the electrical plug off the fan and wired it to a fuse, regulator and toggle switch. Worked. Now the A/C compressor doesn't run. No power at fuse box terminal. Put everything back to original, still nothing. Is there another fuse or relay that could have blown?

__________________
1984 MB 300SD Turbo

They did a design change to the systems on the 126. The models up to 1985 share the electrical and climate system found in the 123. The 86-up models use the 124 style systems.

The older blowers used on the 1985 and older were controlled from a relay box that switched different resistors in line to the motor to vary the speed. The 1986 and up use an electronic regulator to send a PWM signal to the motor (sends a square wave with different off/on proportions based on desired speed).

I would obtain the electrical manual for the car. Last time I checked, MB still had this up on Startek. If you can't find it, the circuit for an early 80s and up 300D should point you in the right direction.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Here's the link to the startekinfo w126 manual. I'm not sure if you need disk 1 or disk 2, you'll have to look through both to find your car. The w123 one works well for me, so it should be fine.

__________________
1984 300TD -- summer daily driver
Many others that aren't Mercedes...