| Re: [GMCnet] Bought that new electric clutch for the engine fan. [message #330250 is a reply to message #330243] |
Fri, 23 March 2018 16:33   |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
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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
Foolish Carriage, 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
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