Since this was my mess in the beginning, I'll step back in here.

There are two types of fans for the 203 chassis C-class.

Each style has the same four wire plug. the wires are:
1) Big power input. <~~~ must handle 50+ amps!
2) Big power ground. <~~~ must handle 50+ amps!
3) Little signal input lead. <~~~ tiny little thing.
4) Little feedback lead. <~~~ tiny little thing.

One has wires leading from the plug directly to the fan motor.

<~~~~ best fan!


The other has a large visible heat sink between the plug and the motor.

<~~~~ dies with 12 volt feed

<~~~~ No direct 12 volt!

The fans with a visible heat sink will die in just a minute or two of full 12 volt connection to the small input wire.

Either type of fan can be used with Hooziewhatsis's fan controller.


Mercedes has a habit of over engineering everything. The fans have all the logic and run speeds built into them. The car simply tells the fan to run at speed #6 or run at speed #12. The fan looks up the requested speed on it's on-board logic circuits and controls it's own speed.

When you feed the more desirable fan 12 volts directly to the input lead it will think there is a problem and default to full speed.

The fans with the heat sink do not have the circuit protection. Feeding them a direct 12 volts to the input will fry the on-bard electronics and burn up the fan.

When developing the controller offered by Hooziewhatsit we spliced an o-scope into a Mercedes wire harness to capture what the car was telling the fan. Hoozie then replicated that signal using the temperature sensor readings.


Rest assured that if you have air flow issues that fan will solve it. Andrewh laid a fan on top of his engine (resting on the intake and radiator) and it kept the engine cool for over 30 minutes of idling in his driveway.