Bought that new electric clutch for the engine fan.

[billvv]

I have been told that the controller for the Mercedes Fan Clutch sends a frequency signal to start and stop the fan, and that you cannot wire the fan
leads directly into an EFI system dry contact output or an ON-OFF switch without the controller. Is that correct?

The reason I'm asking is that I wanted to have a fan along on my trip to the Tucson rally for backup and while Applied has the fans, they will not
have controllers available for another two weeks.

--
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid
November 2015.

 

[johnny]

No, Bill, that information is in error. The clutch engages with 12 volts and ground, and disengages when the 12V or the ground is removed.

That being said, there is a means of recovering fan speed from the clutch, using the three unused wires on the connector. Mercedes - and the other
manufacturers use thi information to regulate the fan speed... in order to squeeze the last iota of efficiency for CAFE purposes. Doing this on our
coaches is being evaluated as I write. It's my gut reaction that it will complicate the system with little or no benefit in a GMC, but I'm ready to
change that opinion should the evaluation reveal some value. Keep watching this space.

That being said, if you feed the three unused pins 12 volts and ground, the third will produce a pulse train whose repetition rate is directly
proportional to the fan RPM. It will produce six pulses per revolution. If you divide this by 2, you can feed the resulting pulse train to a
tachometer set of a 6 cylinder engine and the tach will read true fan speed.

==JOHNNY
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased