On my 84 300D and my friend's 85 300CD inside the engine compartment on the passenger fender wall forward of the coolant recovery tank is a metal boxed item. The box has numerous holes in it and through the holes one can see coils of wire.

What is this part? What does it do? How does one know if it is functioning or not?


Dave H...

that is the heater fan resistor box, as the fan is switched to med and slow it adds resistance to the power flowing to the fan. clever, huh? the coils are nichrome wire and get hot when the fan is running in med and slow, so they are enclosed in a ventilated box. clever, huh?

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

WOW what a quick and yet thorough response.

Thanks Much,
Dave H...

Very much like the resistor grids of the bygone era of trolley cars, street cars, and interurbans. In those cases the resistors were used for traction motor speed control. They were generally large cast iron pieces mounted inside roughly foot square ventillated boxes under the car bodies. Twenty years ago found a set of those in a welder's shop being used as a load control on a large welder.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

and you know it works proper if you have all 5 fan speeds. I had one meltdown, and lost 4th.(which seems to be the most used speed by the CC unit)

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1984 123.193 372,xxx miles, room for Seven.

1999 Dodge Durango Cummins 4BTAA 47RE 5k lb 4x4 getting 25+mpgs, room for Seven.

This place is a plethora of information.


Thanks everyone.