horton air clutch for fan on 2007 Freightliner M2 106 with MB engine

Real frustrating problem; the truck runs cool in normal driving,
and then I idle and raise engine RPM to run my PTO for rollback bed
and it overheats. Replaced Horton air clutch about 3 years ago.
I grab the fan blades and they spin easily.
Is this nearly new fan clutch needing a rebuild already?
And can I disconnect the air to make it constantly driven?
Seems simple enough to remove and rebuild,
looks like the prices have doubled in 3 years.
Any thoughts?

 

Only happens at idle.
Fan clutch does not seem to engage at all, even when hot.
(haven't checked air flow.)
I can spin the blades when the engine is off,
which I shouldn't be able to do.
I think air power holds it engaged, then the air shuts off to spring disengage.
Or do I have it backwards?
Anyway, if the blades have no resistance, the clutch is cooked.

 

spins easily, like in the Horton video, with the key off and no air pressure.
I was thinking it is whatever reads temperature and kicks air on at 200 deg.
I do not hear that happening any more.
Apparently there is a sensor that operates a solenoid.
gotta get part numbers when FL opens Monday.

 

Roger that, Thank you, makes sense.
I'll look again in the morning.

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And, now that I think of it, isn't there an improved design
fan clutch out there that out-performs the Horton?
I ran across it before, after I already sent for the Horton.
If you know, shoot it to me, thanks!