I have a 91 300SEL and the blower motor does not work. Since I have a 91 560sel as well, I started to swap parts one by one to rule them out.

Checked all fuses which are good.

swap Push button unit from 300sel to 560sel and it is good & vice versa

Swapped both blower and "porcupine" from the 560SEL (known good working unit) to the 300SEL and still does not work.

The only thing left is the resistor in the engine bay but how in the world do you get to it. I tried removing the fuse box but looks like I will also need to set aside the bulk head as well

That resistor is only for the radiator fans.

Remember that if something is shorted the CCU will go into a safe mode and just power off. I'd start by checking the coolant pump.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Thanks for the reply. After your reply I researched the Aux water pump and that could indeed by my issue unless the wiring to the pump is either open or shorted. I will check that out tomorrow. A new battery was installed earlier this year and given the area where the battery goes & where the aux pump is located the wiring might of been damaged during installation.

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2001 E55

2001 E320 Sedan

2001 Subaru Legacy

2006 SLK280

2016 Subaru Outback 3.6

Did you check the 30 amp metallic strip fuse located near the fuse box? They have a tendency to crack. It's located toward the passenger side of the fuse box. Small rectangular box with a lid. Metallic link is held in place by phillips screws.

Also, There are three wires going to your blower ass'y. Battery positive, ground and a signal from the control to the speed regulator. You should see around 6-8 volts on that one wire if the pushbutton unit is working.

Another possibility is the ignition switch. Try gently moving the key a little and see if the fan comes on.

That was my issue. The fuse looked and even tested fine. But while a volt meter said it was fine it really could not carry amperage right. Once I removed a screw it fell in two.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

There was only 2 wires going to the blower assy on both my 560 and 300 & yes the Push button unit is working since I swapped them from car to car. I looked at the strip fuse which looks ok but I will actually remove it from the box and look at it closer.

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2001 E55

2001 E320 Sedan

2001 Subaru Legacy

2006 SLK280

2016 Subaru Outback 3.6

You can check for +12 volts on both sides of the strip using a test light or voltmeter.
Much quicker than removing it.

Which will give you voltage but no hint as to the amperage it can draw.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

I took the strip fuse off and it looked ok but as soon as I touched it, the strip disentgrated into 3 pieces. I will order a new fuse, thanks for the help

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2001 E55

2001 E320 Sedan

2001 Subaru Legacy

2006 SLK280

2016 Subaru Outback 3.6

I don't think they are Benz specific. I found one locally for 50 cents. Any specialty electrical store may have one.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

If the circuit is open (voltage on one side but not the other) there will be no current drawn.

Speaking of current... Make sure you get the correct value link. I would just go to the dealer to be sure.

I ordered a new fuse kit and several 30A strip fuses for spares, while I am waiting, I took the known good strip fuse off my 560sel and installed it to the 300sel & the blowers still do not work. The strip fuse holder looks good with no corrosion. I traced the 2 leads to that fuse as best as I could and it looks good and did not find any opens or corrosion on them.

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2001 E55

2001 E320 Sedan

2001 Subaru Legacy

2006 SLK280

2016 Subaru Outback 3.6

Do you have 13.8 volts at both ends of the fuse?

That got my blower going on my '84 SEC.
Going to change the ignition switch behind the key cylinder as soon as I get the courage to remove the cluster.

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OLD & RETIRED
_.... Don't mess with old farts - - age and treachery will always overcome youth and skill! Bulls**t and brilliance only come with age and experience!____________
'96 E320
'79 450 SEL
'78 300 CD