How to test the electro-viscous fan clutch

Mooseman

Master Blaster
Original poster
Moderator
Dec 4, 2011
22,550
Ottawa, ON
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.
 
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bigoilman

Newbie
Sep 7, 2019
3
Ocean Springs, MS
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

Guru
Aug 16, 2015
2,074
Colorado
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

Newbie
Sep 7, 2019
3
Ocean Springs, MS
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?
 

Mooseman

Master Blaster
Original poster
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Dec 4, 2011
22,550
Ottawa, ON
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.
 
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TJBaker57

Guru
Aug 16, 2015
2,074
Colorado
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.
 
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TJBaker57

Guru
Aug 16, 2015
2,074
Colorado
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

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Dec 4, 2011
22,550
Ottawa, ON
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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Mooseman

Master Blaster
Original poster
Moderator
Dec 4, 2011
22,550
Ottawa, ON
A quick addition to this. The method of jumping the relay can also confirm a dead clutch that freewheels and offers no resistance when stopped with a rag. With the engine running, pull the fan 'relay' and jump the two slots as the the pics. Wait a few minutes and the fan should start pulling air hard. Rev the engine and it will try to take off. If it continues to freewheel, it's toast.
 

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Mooseman

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This is a video by SMA that explains the fan operation and a failing Hall Effect sensor. It also sounds like it's pulling too much air when it's being commanded not to.

 

aaserv

Platinum Donor
Dec 1, 2019
351
N of Baton Rouge, La.
Just as an addendum to previous posts.........The problem Ive found with virtually all the replacement fan clutches is that as seen in the videos here the fan clutch is almost constantly changing speeds and the cheaper replacements don't seem to be able to change fast enough to keep up. Especially they are very slow to increase speeds when needed.
I got a couple of $65 fans off ebay thinking they would be fine for use while i was working on the car and not really driving it more than a few miles at a time. They didnt work at all!! Tried a couple more with same results. Ended up using OEM fan from a junkyard and they worked much better than brand new ones from the local auto parts.
I think a lot of problems stem from the cheap fans. People replace their good OEM fan with the parts store special thinking theirs was bad and they have now compounded their problems because they now still have their original problem plus now the cheap fan that cant keep up...

As of the time of this posting I still dont trust the newer ACDelco products, they seem to possibly be using rebranded overseas junk like everyone else. But thankfully the BEHR company who made the original OEM fan is producing these fans and they seem to be readily available from Rock Auto and others. They are priced lower than the ACDelco and we know they will hold up to the high stress needed on these vehicles.
In the words of the great Billy Joel........."Get it right the 1st time thats the main thing" :2thumbsup::2thumbsup::woohoo:
 

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