Okydoke, today I connected the fan I acquired from a C class to an ML to test it. The plug was identical however the wiring colour on one lead was different. The C class I have had the heavy red and Brown cables, a thin black and white and a green and blue, on the ML the wires were the same with the exception of the green and blue, on the ML the cable was yellow and blue. Keeping in mind this is a customers car and I did check with him to see if it was ok to use it as a guinea pig.
So before doing anything we tested his fan, the engine was fairly warm, after starting his engine the fan did not come on for three minutes or so, when it cut in it was very quiet, the temperature did not rise and we gave up after ten minutes or so. Switching on the AC the fan speeded up but I would not say it was full speed, The AC was cold, the fan slowed once or twice and then picked up again, I am unsure if the AC ecu controls this via condenser temperature sensor or trinary switch as per my car.
So we pulled the plug and with the colour difference in mind plugged it into my C class fan, started the engine and the fan started up in less than a minute, about two minutes in and the fan gained some speed, obviously the ECU had detected the engine is not being cooled correctly, switching on the AC the fan again stepped up the revolutions. We shut down the engine as we did not want to risk overheating it.
We then put the plug back where it belongs, the ML fan came on within about ten seconds and it was clearly spinning faster than it was at the beginning of the test however, in less than a minute though it slowed down again to become almost silent, AC response was the same as before.
Observations:
Cable colour difference, unsure if this was the trigger wire or what?
The ML fan is bigger both in diameter and blade count.
The C class fan was noisier but it was being held near the front corner of the ML to reach the plug, there was no obstruction to airflow so that may be the reason?
The ML fan is 850 watts.
I forgot to measure the centre mounting bolts, but there are four the same as the C class, possible to swap motors in the future?
So, whilst my fan did not spool up to full speed as the ecu decided it was not needed, I am for the moment calling the fan good, and this weekend will see the radiator pulled out and see how well the fan fits.
