Not an expert, here or on TV. Pretty good at rolling around on the creeper with 16 inches of ground clearance LOL.
Yes this is all true. The fan spins when the engine is running. The difference characteristics sounds and power required of a free wheeling verses an engaged fan can be demonstrated on a
cold engine.
In a
correctly working system... cool engine running, pulling the connections to solenoid valve, TDM or a temp sw lead should engage fan.
It's a bit subtle... so a couple of plug in's and wait wait wait and pull's and watch and listen... for it. Having one work the throttle a little helps to get the effect you looking for.
Note: Key to proper temp / fan cycling is the "electrical temperature switch" in the water crossover manifold. Think of it as the heart beat to the rest of the system.
The TDM and control valve follow along if all are working correctly. Correctly is the BUZZ word, as a malfunction requires a little more probing. These tests can quickly determine which parts need replacement. The free little Hummwv manual will get one pointed in the right direction. Wish I had a dollar for the times I linked to it here. >
https://gear-report.com/wp-content/uploads/2017/03/HMMWV A1 Troubleshooting.pdf
Failure is not the option were looking for on the HumV fan circuit.
Here a little observation. Every Spring / Summer, overheating FAN issues. Come around to late Fall /Winter, white smoke and glow plugs.
New first timers... anything goes. The cycle of HumV I guess. Just saying, CAMO