How to test the electro-viscous fan clutch

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Mooseman

Mooseman

Moderator
Disengaged would be the default no power applied condition on a working clutch so no PCM is required. If you applied full power to it and it still doesn't engage, it's toast.

You say ypours completely stops with the engine running? That is practically impossible unless something is rubbing on the fan. There is always some friction that will make the fan turn a bit. either way, yours is definitely done.
 

bigoilman

New Member
Disengaged would be the default no power applied condition on a working clutch so no PCM is required. If you applied full power to it and it still doesn't engage, it's toast.

You say ypours completely stops with the engine running? That is practically impossible unless something is rubbing on the fan. There is always some friction that will make the fan turn a bit. either way, yours is definitely done.
That's my thinking too. And, yes, it will come to a complete stop. Shocked me too.
 

TJBaker57

Well-Known Member
no tug of the clutch engaging to be felt. Jumped the relay socket, and no change there either.
Disconnect at the harness and check for a resistance between the clutch 12vdc terminals. Black and White wires if memory serves. If you can reach in through the fan blades and wiggle the harness connector at the clutch end watch for the ohmmeter to jump around. I found mine had loose pins in the connector at the clutch end. I had to give a slight twist to the pins (see post #36 above in this thread) to get good connection and now mine works.IMG_20190829_105159.jpg
 
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bigoilman

New Member
Is there a way to test the clutch with it off the vehicle? I'm gonna check resistance as indicated in the post above, just wondered if there was a definitive way to tell if it works?
 
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Mooseman

Mooseman

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Off the vehicle? Not that I know of. They usually fail electrically internally. The odd time they also lock up permanently when the bearings seize.
 

TJBaker57

Well-Known Member
FWIW, I had 10.5 ohms at the harness end secured to the shroud. After the repair that is. Before it jumped all over as i wiggled the connector at the clutch. What led me to test this was when I commanded the fan to full engagement with a tech 2 it worked once or twice but failed many other times. So I knew at least the thing worked. Just had to find the intermittent.

Edit: off the vehicle when I connected 12 volts to the black & white I could hear the valve mechanism click inside the clutch.
 

TJBaker57

Well-Known Member
Just came across this exchange which adds a couple of details often omitted from discussions of fan clutch testing. The running of the engine at 2000 rpm for 2 minutes is often neglected. In my tests I have seen that these fans engage rather quickly but they do take significant time to disengage afterwards. Maybe someday I will tear one of these clutches apart to see just how it works internally.

The "pin drag test" seems like something that could be useful in a wide variety of electrical/wiring troubleshooting, although I think I'll continue my ohmmeter-based resistance check with wiggling the connectors. But in multi-pin connectors my wiggling just might not detect some faults.

 
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Mooseman

Mooseman

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The pin drag test is a good test for just about any circuit checking. There have been instances of loose relay and fuse connectors in the fuse box. A quick solution to that is to give the pins a slight twist.

That particular guy's issue was likely a bad hall effect fan speed sensor in the clutch itself despite being new. The fan engaged when 12V was applied and disengaged correctly, but when operating, it would engage more than necessary probably because the sensor wasn't giving the PCM the true speed and thus would try to speed it more to get to the commanded speed. That's why we never recommend store or unknown brand clutches. That's why we always recommend either Hayden or Behr/Hella/ACDelco.
 

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