Blower motor resistor problems


New member
The resistor in my 2003 Sprinter 2500 keep going bad after a few hours. I have replaced 4 in the last month. Does it have something to do with the blower motor ?? The van is modified to carry my wife who is a quadriplegia with MS so I really need the heater/ac in working order. Can anyone help me solve this puzzle ?

Aqua Puttana

Poly - Thread Finder
First let me extend you a hale and hearty welcome to the forum. welcome2.gif

That is too many failures for things to be normal.

My first guess would be some sort of harness/wire problem. Some people have had problems with critters getting into the engine bay and chewing wires. Poor connections or grounds may cause local heating. Do the resistor connections proper show signs of heating or melted insulation? A problem there would transfer more heat to the already hot resistor assembly.

Another possibility might be that the blower motor bearings are going bad which might put additional load on the blower supply. The blower fan is available to the left of the engine bay. You should be able to reach in and spin it with your hand to see if it seems tight or moving freely.

There is a cabin air supply filter under the hood near the center. That could be plugged and restricting air flow which is used to help cool the resistor assembly while in use.

Good luck.



Haulin' A** since 1974

I just replaced my van's 2nd resistor in 2 years last week and took the opportunity to pull out the fan motor - because I read somewhere on this forum that it was a good idea to lube the bearings and such. Apparently a motor that is getting old or dry can cause resistors to shorten their life.

I was able to get the motor out of the housing, apart from the fan blades... with a lot of grimy cussing... but it is a sealed unit and there is NO way I could see to lube any bushings or bearings without further tricky disassembly. I squirted some TriFlo at the shaft and put it all back together. Not sure it made any difference. But it is working on all 4 speeds for the time being.

My recommendation is to replace your cabin filter, check that there are no other blockages in the vent system, and if no other problem is found... spring for a new OEM fan motor. IIRC, they cost about $150. But at the rate you are buying resistors, that may be a bargain.


Erratic Member
Here's a screen grab of an old thread.
Note the cylinder on the left side of the resistor.
That's a "thermal fuse" .. and when it pops, the motor stops.
You could replace it with a (not too much) higher-rated fuse, or at least with the 420F part listed in the text:


good luck


Mercedes-Benz Resource
Hi there,
It would be a good idea to have a close look-see at the plug in connector and its spades. Often due to the placement of this device weather/moisture etc gets to work on the contact spades. Corrosion causes some low resistance to the joints and secondary heating occurs (Quite large current is drawn by the blower motor - check out the cable size!)

One or two things could be happening here:

The extra heat produced from the tarnished corroded spades in the connector is adding to the heat produced in the 'dropper' itself thus terminating it more quickly due to overheat - or the other units are not faulty (assuming they are not obviously visibly blown apart!) and you could have a reoccurring poor connection in the connector.

Additionally - I would not totally discount an intermittent motor with a dead-spot on the commutator/poor brushes, especially if the other speed control resistors were found not to be faulty.

All the best

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