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New Fan clutch Always engaged

30K views 16 replies 7 participants last post by  Int4108 
#1 ·
I had an a/c problem that I just sorted out, ended up being a broken wire in the engine harness going to the high pressure switch. The fan started intermittently engaging even when engine was cold, but not its always on. I did swap out the clutch for a new one while i was working on the a/c system and this new clutch is no different to the old.

I thought the high pressure switch had something to do with the fan clutch operation by reading through some threads, but if there was another wire broke in the engine harness where it goes by the alternator down to the switch, wouldnt the a/c still have an issue?

Temperatures are a non issue, i monitor my temps ALWAYS, but the clutch is locked even when dead cold.

My next step is to test the wire integrity supplying the fan clutch. If all are good then will move to the loom that leads to the high pressure switch to look for broken/stretched wires.

Any thoughts or suggestions?
 
#4 · (Edited)
update:
Checked all wires from fan connector to pcm plus the hot wire, all good. Moved to the high pressure switch and checked intergrity of ground, circuit wire from low pressure switch, and pcm wires, all good. tried a brand new high pressure switch, no change. EGR is deleted but egr is plugged in. Also does it when a/c turned off. In other words, always on except when truck is off.

What else can cause the fan to always be on when truck is dead cold?
 
#9 ·
Shot in the dark but pop the powerstroke emblem off the fan shroud and start it. Check to make sure that the front metal plate isn't bent. I've had a defected one like that. Fan would spin freely and all. I guess the slightest bit of current would lock it in.


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#13 · (Edited)
Being a PWM signal, the best way to read it is with an oscilloscope. The pic below shows (roughly) the look of the voltage that the PCM is sending to the fan controller in time. Just ignore the "analog write" stuff.





So... the top graph is 0% duty cycle. That would be the fan being commanded full on. The bottom graph is 100% duty cycle. That is the fan being commanded full off. The intermediate PWM duty cycles are the kinda off/kinda on states.

The problem with looking at PWM signals with a volt meter is that the voltage that you get depends upon the input lowpass filtering (if any) of the meter. Add to this that the actual 6.0L fan PWM signal looks like garbage compared to what I have shown.

You may do okay for measuring intermediate values, but the full on/full off voltages could be deceiving.

I haven't read your thread at all. I just saw @ZMANN 's comment and your response. I'll look back.

Hope this helps.

______________________

Edited to add...

Okay. Read back.

Another reason why you maight not be seeing things correctly is because - as near as I can tell - you are looking at the voltages without the fan plugged in. As @ZMANN said, the high voltage potential is being supplied through a separate pin on the fan connector. The PWM command signal is basically an intermittent ground controlled by the PCM. In that case, you would not see anything because the ground is being switched without a high voltage to be grounded.

I'd be looking at the signals with the fans connected. I realize that is not terrible convenient. A sewing needle can help. ...or probing through the back of the connector.
 
#14 ·
I did see it cycling when I tested the connection with the plug apart, obviously i couldnt measure the pulse rate other than it cycling every few seconds.

I ended up having to take the truck on a trip 2.5hr away on friday. For the first 1.5hrs the fan was locked up 100% always. Then I noticed it was normal for about 10 minutes, then it began cycling on and off pretty quickly for a couple minutes, and then maybe locked up a couple times during the last hour but not for long. On the 2.5hr drive back, it was locked up for a few minutes when cold, then noticed the fan only a couple times the rest of the trip. The trip was a lot of highway driving. Yesterday, was locked up for about 30 seconds when cold, and didnt noticed it again, only drove for about 1hr total.

Not sure what caused this or is causing this still. I will update if it continues or gets worse. Right now its looking like its steadily improving.
 
#15 ·
if it runs fully engaged unplugged it is fubared

and it sounds like it is engaging too much the way you described it
as you should never really hear it unless it is super toasty or the PCM commands it due to a certain parameter like hot tranny , certain OBD codes, High AC psi etc


Electro-Viscous Cooling Fan Clutch ( vistronic) clutch
just heat at the clutch without a PCM signal can activate it also
 
#16 ·
I had the exact same issue, I bought a fan clutch from oreilly and the fan would run when the AC was on continuously. After checking everything, pressures EOT harnesses I replaced it with an Autozone fan clutch and the problem went away. The fan clutch from oreillys checked out good with no codes but was bad. If I were you get an OEM fan clutch. Took me months to figure this out. Hope it helps
 
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