Fan Clutch

On my 2002 Trailblazer, I don't think my PCM is "telling" my cooling fan clutch to "come on". I have replaced the fan clutch and it's doing
the same thing as the old one. I can see the fan turning but I can never HEAR the fan turning, (like I used to), even when the temperature gauge moves up to 230 degrees in traffic, and returns to normal when I start moving again. How can I test to see if the clutch is "getting the message" or not?
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Greetings,
I can't say specifically about your Trailblazer, but on most vehicles where the fan is mounted to a clutch and then to an output shaft that is turned by the engine (as compared to a seperate electric fan mounted directly onto the back of the radiator) there is no electrical connection between the clutch and the ECM. The clutch either engages or disengages based on the ambient temperature it senses itself and nothing more.
A typical fan clutch has an 80:20 engagement ratio. In other words, when the clutch is disengaged there is about 20% of the power of the shaft still turning it (the fan still turns but not with any great force) and when the clutch is engaged there is about 80% of the power from the shaft turning it (the fan spins with speed and force but still has a little "slip" to it).
If you go under the hood with the motor off and cool, reach around the fan shroud and spin the fan blades by hand. If it spins easily and takes more than a revolution or two to stop then the clutch is most likely bad. If your temp is rising to 230 at idle and dropping back down to normal when you are up to highway speed, I would suspect the clutch - again.
Good luck - Jonathan

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The pcm controls a high and lo engagement on this fan, a full scan will see if the pcm commands these controls, when the temp reaches about 225, the fan shouuld engage into the high operation ,some AM clutches are having issues with this.

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Greetings,
I'm going to claim ignorance on this one, which most certainly won't be the first time - or the last. What I'd like to know is if the fan clutch is mounted to the pulley for the water pump or some similar arrangement, and if it is then how is it wired? Or is the fan electrically powered and hard mounted to the shroud on the back side of the radiator. None of the computer generated/enhanced photos on the Chevy website show this clearly. The one image in the Trailblazer section shows the front of the SS motor without the fan, but since the OP has a 2002 then I don't think this is the right motor anyway.
Cheers - Jonathan

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Trailblazers are funny beasts... the fan is mounted to the crank, and on the front side, there is an electrical connector that spins around.

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All these technical answers when the simple answer is he has blown his hearing with the boom box so he naturedly can't hear it like he used to...

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