Needle has went all the way past 100. I'm guessing 110 psi with fan off.
You can guess, bet, flip a coin, get out a weegie board... bottom line is somehow your not reading the posts here or taken the time too... HERE GOES... look in the TM.
IF ALL THE COMPONENTs ARE WORKING CORRECTLY...
Normal NOT HOT
On a cool engine ie 215 degrees (but for test sakes cold start) Engine running, engine temp switch CLOSED, 24 volts being applied to TDM from temp switch, 24 Volt now applied to solenoid, your indicated plus 100 PSI (good) at the gauge location in picture, fan should be disconnected more or less "freewheeling" (Don't try and grab it)
Going hot 220 +/- degrees. ( dependant on individual OEM temp switch quality control / design characteristic and maybe engines ??)
At set point of switch design... Temp switch OPENS, Breaking flow of 24 Volts to TDM... in turn removing 24 Volts to solenoid and removing pressure, allowing clutch springs and linings to lock fan to drive belts and suck BIG air thru radiator, over the engine, thur the tunnel, raising the cab temp and rattling your ears. YEP, been there, felt that, heard that.
TDM Kickdown / switch. Should fan be engage (HOT ENGINE, NO VOLTAGE TO SOLENOID) and driver depresses throttle to the floor . A switch will close and triggered the TDM to provide 24 Volt for about 20 seconds to disconnect fan... allowing extra ponies to say pass or ease the truck / fan into water before becoming a propeller.
Note: This switch (kickdown) also signals / controls the 3L80 to down shift. 4L80e is too damm smart. TPS
Failsafe mode. Electrical disconnecting of components will place fan in the engaged state. (good to know if can't control overheating)
Again, all components fully functional and best to be OEM. DIY and hacks...all bets are off.
That's how MY fan system works. Others... I have not a clue and folding while ahead....Before mine breaks. LOL
Mr. GRUMPY and HumV are going for a COOL ride, GRUMPY