Roughly what temp should the fan clutch engage at?

[The Warden]

After a scorching hot day yesterday that proved to be too much for the a/c and the coolant (with the a/c on, the coolant temp got up to 100°C before I shut the a/c down to prevent overheating; the coolant dropped back to normal after I killed the a/c, although I also need to do a cooling system flush). Granted, my electric fan doesn't work and is probably contributing to this, but I realized that I don't think I've ever heard the engine-driven fan kick in. I have an idea of what it should sound like (you should hear my truck when the fan kicks in; it sounds like a jet engine taking off!), and don't believe I've ever heard it. Spinning the fan by hand, there's some resistance, but I guess it isn't enough.

So, I think my fan clutch is dead...any reliable way to confirm this beyond a shadow of a doubt? Also, there isn't by chance an aftermarket supplier that makes electromagnetic fan clutches (such as this), is there? I like the idea of the engine fan sensing coolant temp and going from not-moving-at-all to full-speed-ahead without dragging any...

Thanks in advance!