Heater Blower Resistor Location

[gcw206]

My heater blower in my 1969 280SE Coupe W111 will not work.  The fuse is good, and I am trying to locate the series resistor, but am having no luck.  Where is it located, and how do I test it?

[Aaron h]

In a W111/W112 coupe`/cabriolet the heater fan switch is the actual resistor.  There is no remotely mounted resistor.  Remove the phenolic plug from the front of the heater case and test for continuity or excessive resistance across the motor itself.  At the same time, also test the plug itself to insure that the blower switch is supplying 12V+ in the "hi" position (all the way to the right, last detent), and that the voltage varies when the knob is turned counterclockwise.  And last, confirm continuity of the ground for the circuit. 

Theses switches rarely go bad.  The blower motor itself is what usually quits working having seized up. 

[gcw206]

Thanks, that answers my question.

[Aaron h]

You're welcome!  Do let us know of your progress and what you find so others reading can benefit from the completion of your adventure.  I, myself, will be curious a to what problem(s) you find. 

[gcw206]

Hello,
You were 100% correct; the fan blower motor was/is dead. Is there an easy way to replace just the motor w/o full blown open heart surgery? 
I don't want to remove the entire plenum if at all possible, just r/r the motor.
Thanks agin for your input,
Galen

[Aaron h]

No, unfortunately there is no other way to replace the motor without having to remove the whole heater box from the car.  It's not a particularly difficult job on a W111/W112 coupe`/cabriolet.  It's more time consuming than anything.  Just take advantage of the heater box being out to renew the heater hoses, grommets through the firewall, and having both heater cores cleaned out internally.  You'd be amazed at how much dirt and silt settles in the bottoms of the heater cores impeding coolant flow. 

The blower motor is no longer available new, but for ease of your searching the part number is 000-835-09-02, and the same blower motor is used on all W111/W112 coupe` and cabriolet, W111/W112 sedans, as well as all W110 cars.  I recommend searching for this blower motor under the W110 because anyone selling a blower motor for a W111/W112 coupe`/cabriolet will likely charge more ONLY because it came from a W111/W112 coupe`/cabriolet.  99% of people don't know that this blower motor was used in many other models. 

[austinado16]

New member here, so I hope I can add a little info without offending anyone.

I'm currently rebuilding the heater unit in my '66, so thought I'd share what I'm seeing with the heater boxes:

-The small motor used in the W110 cars is physically smaller, has a smaller diameter blade shaft, and uses a blade with a matching small diameter hole in the center.  This motor also only uses 2 of the 3 prongs for it's electrical connection, and it's 2 mounting studs are a different spacing than the variable speed motor used in the W111.

-It appears there are at least 2 different larger high output motors for the W111 cars (or there could be more?).  These are both physically the same, have the same 3 prong electrical plug and the same shaft diameter, and hole through the fan.  How they differ is in the 2 studs that mount them to the frame of the heater box.  My '66 has a motor with recessed areas where the long motor housing studs come out of the top of the motor.  These studs protrude much longer than the version of the motor that doesn't have the 2 recessed areas and it makes fitting the non-recessed motor a challenge.

-The W111 fan appears to like to split apart, right in the area where it has 2 upside down V notches that locate it on a split pin that is pressed through the motor shaft.  This doesn't appear to be an issue with the W110 fan, because it has a smaller diameter hole through the fan, allowing that area of the fan hub to be thicker, and stronger.  I think you could drill out a W110 fan if you had a drill press and could keep your drill bit running true.

-The fans can be very tough to remove because the motor shaft rusts inside the plastic fan hub, and grips the hub for about 2".  My method of removal was to use Kroil, sprayed down the shaft, and with the snap ring and spring plate removed from the shaft, I reached down through the fan blades, grabbed the bottom edge of the fan hub with my fingers, and hung the entire heater box by my left hand.  I then started smacking the motor shaft end, with the nylon handle of a large screwdriver.  Ultimately, I used a hammer on the shaft and once I got the fan moving, I tapped the fan back down the shaft, added more Kroil, and repeated the process (moving the fan up and down the shaft) until I could get the fan to come up off the shaft partially.  Then I inserted a punch between my fingers (a 2nd person would have really made this easier), and started striking the punch with a hammer.  That did the trick.

-The front panel of the heater box is different between the W110 and W111 models, and it will be painted with white letters/numbers, as to whether it's for a W110 or W111.

My original motor was partially seized with rust, had cooked the rheostat in the blower switch, and had also started immediately blowing the fuse out in the engine compartment.  Initially I jumped on ordering a really nice heater unit labeled "W110" in white factory paint just above the electrical plug-in, because the ebay seller said it also fit the W111 models.   I ordered it, waited almost a month for it to arrive from Denmark, and then discovered that there are quite a few differences.  Not a total waste of money because it provided a lot of spare parts, but still...a waste of money.  Had I just purchased a W111 labeled heater, or just a W111 correct fan motor (which I ultimately had to do) I would have saved a lot of money.

Anyway, I hope this helps, and I hope I didn't step on any toes.

[Aaron h]

No, no toes were stepped on.  Different views and insights are always welcomed!  Though, I have to disagree about one thing though.  The early W110 motors weren't single speed, per say.  While there were physical differences between the motors, (early vs. late, not necessarily W110 vs. W111/W112) The early W110, W111, and W112 sedans had a two position "pull out" switch that gave you only high and low. Sometime in late1965 Mercedes started using a variable potentiometer type rotary switch on the W110, W111/W112 sedans, as well as W111/W112 coupe` and cabriolet that gave more than just low an high.  The speed was infinitely variable from low all the way through high. All the motors were technically a one speed motor when a full 12V was applied to them, but it was the switches that allowed for the different speeds.  The differences you're seeing in the number of pins in the plug connections was due in part to the introduction of the infinitely variable speed switch as well as the "high output" heaters verses the standard output heaters.  The number of wires going to the fan motor wasn't necessarily a chassis specific issue, but more of an result of the cars domicile. 

Below are three pictures.  The first picture shows the early W110/W111/W112 sedans and early W111/W112 coupe` and cabriolet models with the standard output fan and two position "push/pull" switch, picture two shows the W110, W111, W112 sedans, as well as the W111/W112 coupe` and cabriolet models with the high output fan with the two position "push/pull" switch, and the last picture shows the late W111 coupe`/cabriolet with the high output fan and the infinitely variable potentiometer switch.  Picture three is also reflective of the late W110 sedans with the infinitely variable switch and high output motor. There is an electrical reason why the high output motors had three wires and why the standard output motors had two wires.  Those reasons I shall leave to the more electrically inclined to comment further on. 

[austinado16]

Thank you for detailed explanation, AND for the 3 wiring diagrams.  I probably should have taken my unit out and completely apart, and then started shopping for parts or complete units, rather than looking at a few pictures on ebay and thinking, "Hey, that's like mine. I should buy it."  Not a complete waste, but it would have been nicer to purchase exactly what I needed on the first go-round.

I was able to wrap up the rebuilding of mine today, and it's back in and working.  Absolutely no fun, from start to finish!

[Aaron h]

Haha.  I told the original poster of this post that replacing the blower motor wasn't a pleasant job.  He'd asked if there was an easier way or a short cut.  I still say that Mercedes dangled these heater boxes from a string at the factory and built the car around them. haha

[austinado16]

I think the wiper transmission came down the line, suspended by string, first.....followed seconds later, by the heater box.  Good thing I'm a small guy, and fit.

[ja17]

Yes, quite a job. However the linkage assembly for the wiper shafts actually is installed before the heater box. So hopefully you checked the wiper shafts while the unit was out. The Finback sedan version of the heater box assemblies was nearly the same, but is about 1/2" taller than the coupe/cabriolet heater box assemblies. I actually got the longer sedan unit to fit and work fine in a cabriolet some years back. I had to scrape all the sound insulation off the tunnel to get just enough room for it to squeeze in, but it was tight!
The W108 and W109 Mercedes V-8 sedans of the era with A/C were even more time consuming by far, for heater assembly replacement.