...AC Blower Motor Question... - PeachParts Mercedes-Benz Forum

Willie B · #1 07-09-2010, 12:42 AM

...In my 1987 300D the blower motor has abruptly quit... ...The compresser itself is still working...The #7 fuse looks good as do the rest... ...Could the blower motor be fused externally in addition to the fuse in the box???...

...Where is the blower motor located,...so I can check for voltage to it???...

...Also is there a Haynes manual for the diesel version of this car???

Thanks

compress ignite · #2 07-09-2010, 12:55 AM

First Here:
http://w124-zone.com/downloads/MB%20CD/W124/Main.html

Then Here:
http://w124-zone.com/downloads/MB%20CD/W124/Index/602_603index.html

Thanks to gsxr for this:
"First - I assume you mean the heater/AC fan motor, located under the windshield wiper. Right? In that case:

Only the late 1987 300D's have the external 30A strip fuse. Early models (like mine, built in May 1986) still have the 25A fuse in the fuse box. Yours probably does too. Check that first. Cars after a certain date (late '86, early '87) all have the external fuse, all the way to 1995. But 1986 and early '87 models do not.

There is NOT a relay for the climate control blower. It connects directly to the speed controller, aka "porcupine", named such due to the way the finned heat sink appears. That is located underneath the fan itself. If it was working OK before, it's not likely that it suddenly failed."

sasquatchgeoff · #3 07-09-2010, 12:57 AM

Many threads on this subject in the DIY section:

http://www.peachparts.com/shopforum/showthread.php?t=212324

Willie B · #4 07-09-2010, 01:57 AM

"First - I assume you mean the heater/AC fan motor, located under the windshield wiper. Right? In that case:

Only the late 1987 300D's have the external 30A strip fuse. Early models (like mine, built in May 1986) still have the 25A fuse in the fuse box. Yours probably does too. Check that first. Cars after a certain date (late '86, early '87) all have the external fuse, all the way to 1995. But 1986 and early '87 models do not.

There is NOT a relay for the climate control blower. It connects directly to the speed controller, aka "porcupine", named such due to the way the finned heat sink appears. That is located underneath the fan itself. If it was working OK before, it's not likely that it suddenly failed."[/QUOTE]

...Yes the heater A/C blower... ...My car shows a manufacturer date of 10/86... ...It does have the external strip fuse... ...I was under the impression that the blower motor does have a relay, as when on high the motor does not come on until you have traveled about a mile...

...Connections at the strip fuse were poor at best... ...One end had started to melt the plastic... ...I thoroughly cleaned the connections and can hear some cycling that may be coming from the control unit, but the blower motor did not come on...

...I will wait until morning to see if the blower comes on in the high setting after a drive it ...
Thanks Again

Rob124 · #5 07-09-2010, 01:14 PM

I'm thinking my blower **needs** a 30 amp fuse, following yesterday's event. About 2 years ago, my blower failed, and I found the original 25-amp fuse melted into the fusebox--and it had partially melted the plastic around the fuse holder. I moved the blower circuit to an unused position in the fusebox, and put a new 25-amp fuse in. All seemed well.

Yesterday, this replacement fuse began melting, causing intermittent blower action. This leads me to believe that either my blower is drawing too much current, or that 25 amps is insufficient. I'm tempted to replace the 25-amp fuse with a 30 amp device, if one is available. But maybe a better solution is installing an outboard fuse, as Mercedes seems to have done. My car was built in June '86, so has the old setup.

Would it be safe to just plug in a 30-amp fuse, or should I go with a 30-amp outboard fuse? Or do I have a blower problem, although it seems to blow just fine (when functioning)?

Willie B · #6 07-09-2010, 02:03 PM

...As I sift through the blower motor threads it appears as though mine is not an isolated issue...

...In driving the car this morning the blower did not come back on...

...With the engine off, the car sitting, and the key in the on position, I hear what sounds like a real slow turning electric motor from somewhere under the dash... ...It changes speeds for no apparent reason,...from really slow to extremely slow...This is with the fan settings on both high and low???...

...I remember this car having had the blower motor stop about a year ago... ...A couple of days later the blower came back on,...and has worked fine up until yesterday... ...Any body have any ideas???...

...(this is starting to remind me of an XJ6C I had,...erggh)

Rob124 · #7 07-09-2010, 02:16 PM

Have you actually pulled the blower fuse out and looked at the contacts in the fusebox? In my car, the lower contact had retreated down away from the fuse because of overtemp, while the fuse itself remained intact. That's why I had to move the circuit to an unused position in the fusebox.

vstech · #8 07-09-2010, 02:31 PM

the 25 amp fuse itself does not fail, so upping it to a 30 amp fuse would not solve anything.
the problem is the spring that holds tension on the fuse cannot flow 20+ amps continuously and it heats up causing the plastic fuse body to fail.
one of two things will solve the issue. routing the wires to a replacement fuse holder that can handle 30+ amps of constant load, or cleaning the body of the fuse holder and lubing the bearings on the blower motor, and putting a copper CERAMIC replacement fuse in the holder.
choose.

Jeremy5848 · #9 07-09-2010, 02:47 PM

This problem is widely discussed here. There have been several good posts already. Let me try to summarize.

The external 30A strip fuse was/is available as a retrofit to '86-early '87 cars. My '87 (mfg date 7/86) had a PO-added non-MB 30A fuse and a melted #12 25A socket. I installed the factory fuse holder. After awhile, one end actually melted as you have seen. This is due to "ohmic heating" at the connection between the screw (cad-plated steel, maybe?) and the aluminum strip fuse. I replaced the fuse holder and put some non-ox coating of the kind that electricians use on copper-aluminum wire junctions and that seems to have fixed that problem.

The W124 climate control is quite complicated - the description of it covers 30 pages in the 1986 "Introduction into service" manual, when it was introduced. I do not think any of us completely understands how it works. There are schematics of the entire system but not of the PBU internal wiring.

The push-button unit (PBU) in the dash is hardwired (one might use the term "firmware") to wait for certain conditions before turning on the blower. These conditions have to do with outside temperature, inside temperature, coolant temperature, thermostat and pushbutton settings, etc. The possible variations are almost infinite as there are manufacturing variations over the years, PBUs may have been swapped or rebuilt in the past, components may change their values or fail, etc., etc. The high speed blower pushbutton should make the blower run immediately -- high and low speeds have "override" authority, if you will. PBUs have been known to fail; additionally, if there is a short circuit or overload (aux coolant pump being the big one), the PBU will shut down completely (Bosch manufactured) or partially (Kammerer manufactured).

The "porcupine" blower controller is simply a big power transistor or probably a Darlington pair, based on my measurements of its gain. It sits under the blower motor, as was written in an earlier post, such that the heat sink fins are in the air flow to shed heat. This component seems to be reliable, based on forum inputs, which is good, because it costs $200-300!

The blower itself has two squirrel cages and a DC motor in the middle. The motor has brushes and a commutator; these, especially the brushes, can wear such that the motor works poorly or not at all. This is (after the fuse) the most probably failure mode. People have tried to replace the brushes and I believe some have been successful. A worn commutator is hard to repair unless one has a lathe and a lot of experience doing things like that. The motor can be purchased separately from the squirrel cages, made by Bosch, about $100 from Fastlane (click "Buy parts" at the top of the page). In my experience, most junkyard blowers are worn as badly as yours or mine. IMHO, $100 for a blower motor is a good deal.

To access the motor, one must first remove all of the plastic/rubber trim at the center bottom of the windshield, thus revealing the windshield wiper motor/assembly, which must be removed first. Then you can remove the blower and then the porcupine. I'm sure someone has posted photos of this operation in a thread here somewhere.

Jeremy

Willie B · #10 07-09-2010, 03:34 PM

...In searching related threads I found this...

There is a very simple test to see if you have a fuse problem or an ign. sw. problem:

With a 12v test lamp, one lead to a good ground ..w/ other lead , test for 12v on each side at the strip fuse/F-15 [ under small cover near the left strut tower] with key in the ON position..
If you have power to only one side , you have a bad fuse/connection...if you have NO power to either side , you have a suspect bad ign sw contactor bar [ inside ign sw]
The Blower gets it's constant HOT 12v from Bat > ign sw > fuse...
The three wire connector[ X-69 ] is after the fuse and ign sw, so you want to be testing right at the fuse to differentiate fuse or ign sw ..this test will do just that............
One problem with a bad ign sw is that they are usually erratic, so it is best to do this tests when condition exist..I hook the test lamp up and then go wiggle the sw . along with repeated ON/OFF rotation while watching the test lamp to coinside.
And on the fuse test, you want the blower on full position [ Defrost] while doing the test b/c I see these pass a NO LOAD test just fine , but as soon as there is an Amp demand [ Blower] , they will fail..that goes for any poor connection.

...In my case I have no voltage at either end of the strip fuse...From the above it idicates my ignition switch is at fault... ...Has any one had any luck with contact cleaner or Blaster in getting the ignition switch to function properly...

...If that is a negative how hard is it to remove the ignition s/w???...

Willie B · #11 07-09-2010, 07:41 PM

...If I run a jumper from the battery to the strip fuse or from the battery to the 12v+ of the three wire connector behind the brake booster the fan comes on... ...Ergo I do believe it is the ignition s/w... ...for now I will just run an external wire from constant 12v to the in side of the fuse... ...Probably a lot easier than replacing the ignition s/w...