1981 240D

Had an issue with plastic body fuses blowing last year, pulled the motor, cleaned, lubed, checked brushes (totally fine) and issue seemed to resolve.

Driving out of the desert yesterday and the motor wouldn't turn on (cabin switch did nothing). AC compressor is working fine for what it's worth. Checked number 8 fuse, not blown.

Also, I feel like this may be relevant -when the fan was working, and when the heat was on, I got only lukewarm air at idle.
At speed, hot air no problem.

If the fuse and brushes are fine, any ideas what my problem might be?

Model and year of vehicle would be helpful.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

On many models, a seized aux water pump can make the entire hvac head unit shut down. Unplug the pump, if thevsystem begins working you will have thw culprit.

Fuse 8 - I will take a shot in the dark that is a W123.

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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

Apologies, sloppy on my part... 1981 240d

The 240D is very simple. No electronic controls at all.

I had the problem on my 240D where the motor was wearing out and it melted the #8 fuse holder. Fortunately the #5 fuse holder is completely unused on these cars. You can dismount the fuse box (disconnect the battery first!) and let it drop it down under the dash to the floor board. Swap the wires from the #8 fuse to the #5 fuse on the back of the fuse block.

The 240D does not have an auxiliary pump to keep the flow up like the upmodel 300D and the S class of that era. So you will get some cool air at stoplights.

__________________
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

So if it's not the fuse, what might the issue be? Why wouldn't the blower be switching on?

Test the motor with 12V. If it doesn't run, you know the blower motor is bad. Upstream from that is the resistor assembly. Try running the blower on max fan and see if it runs, if it does, the resistor assembly may be bad. Running on the highest speed bypasses the resistors.

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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!)

It is back to basic troubleshooting stuff.

Is the Moter getting voltage and how much voltage?

Is the Motor Ground making good contact?

Mine has a siemens instead of a bosch motor.

Here is a pic of what was wrong with mine. One of the crimped on wire connectors was corroded. A blob of solder over the bad connection restored it.
So problems can show up anywhere in the circuit.

I also lubed it and replaced a bearing. Also there was lots of dirt inside.

Attached Thumbnails

   

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84 300D, 82 Volvo 244Gl Diesel

I'll pull it and have a look... it was a particularly hot day in the desert. Was running A/C on max, pulled in to refuel and by the time I pulled onto the highway, realized nothing was coming out of the vents and that the fan wasn't working.

Tested the motor and it's working fine. I'm not getting any voltage at the connector harness however. What's the next level up?

The switch and resistor pack feed the motor. The switch has 4 states. Off, 1, 2, 3. The resistor has 2 sections - with 3 terminals.

Off - off, no connection
1 - all the resistor in series with the motor
2 - half the resistor in series with the motor (other half shorted by a switch contact)
3 - none of the resistor in the circuit, both halves shorted out by switch contacts.

__________________
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

In theory -if I understand you- switch 3 should bypass the resistor altogether.
I'm not getting current to the fan at any setting.

I think it's time to play "follow the money" with the meter...

__________________
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

Totally, that's my question though. I'm not sure where to look next.
Fuse 8 is getting juice.