Hi all,

I am trying to diagnose a problem with my climate control blower. It works very rarely every once in a while. I removed the blower motor and jumped it to the battery, and it ran. Where else could the issue be? The only other abnormality I noticed was some chewed-off insulation on one of the wires that runs from the connector to the motor itself.

Thanks,
Jack

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Jack
1984 300SD. 115k miles.

Any ideas? Could it be the fan speed switch? How do I remove the veneer to get to the switch?
Thanks

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Jack
1984 300SD. 115k miles.

First I would monitor the voltage to the motor to determine where the issue is. Blower motors of a lot of brands are notoriously intermittent. I have given them a hit more than once to activate them. What did the brushes look like when you had the motor out?

A test light or small meter can help.

Join the club.

Same exact vehicle.

Blower runs fine with 12V.

Blower runs when it feels like it when it is powered by CCU.

More diagnosis tomorrow morning. I'm tired of freezing my ass off.

same here, more on than off, but it'd be nice to figure this one out.

Im pretty sure this is telltale sign of a bad ACC unit.

Only one w123 car Ive had did this, but it was solved by a used ACC from another car.

I think sometimes it may well be just a dirty contact, but apparently the solder joints go bad too.

Still on these cars, the blower current draw smetimes starts to go way high, which is why there is a strip fuse mod. As I understand it, this is due to bad brushes.

So even if it is just the ACC, Id still try to pull and refurb the blower as best as you can...

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Spent four hours on the SD this morning.

Tore the dash apart and determined that the CCU had nothing to do with the issue. Apparently, as the blower gets to the end of its life, it becomes intermittent. Take it out and connect it to a battery and it works fine. Put it back into the vehicle and it works for a few minutes.

Then, it does not work.

Replaced the blower and all is well EXCEPT that I now have full heat.........unmodulated. So, fix one thing and break another.

The blower control and resistor circuitry remains perfectly OK, however.

That doesnt make any sense to me.

So youre saying that with a "firm" connection to the battery, it spins perfectly, but when it connects through something else, that it is intermittent due to being end of life?

That would indicate to me that there is something in the electric pathway that causes an issue, NOT the blower.

Now that could be excessive current draw from the blower... or perhaps the blower cant accept the voltage drop from passing through the ACC.

Just strikes me as odd...

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

It made no sense to me either. That's why I wasted four hours in the rain chasing ghosts.

It was most definitely the blower as the replacement has now operated for 90 minutes continuously without issue. The original blower operated about five minutes before it quit.

I reinstalled my old blower (only change was some electrical tape over the chewed insulation on one wire) and it is running fine... we'll see how long it lasts. I guess it's possible that the exposed wire was touching something and shorting out, but I'm still mystified.

__________________
Jack
1984 300SD. 115k miles.

Grab one at a pick and pull at your convienice. Lower miles looking car if possible. Once intermittent they tend to repeat the behaviours. Only One I hit stayed good on another brand car. All the others eventually repeated their behavious. I figure the one that lasted I loosened up a sticking brush perhaps.