I just started driving a 2000 Freightliner Century Class.

This truck is so worn that the writing on some of the switches is worn off.
Is there a manual switch for the engine fan? If so, where is it located?

I know I could start flipping switches til the fan came on, but I think that the fan may not be coming on like it should be. With the engine running, the fan will spin slowly, (only spins because of the inertia of the fan pulley that is spinning). I took a screwdriver (I didn't want to put my fingers in there in case the fan decided to come on) and stopped the fan momentarily. Then it began to spin slowly again. I did this with the engine temp at 200°. The temp engine never gets higher than around 210°, but I would be a little more reassured if I saw the fan come on every now & then.

If you want to make sure the fan comes on cover the radiator with cardboard to cut off the air flow and bring the water temperature up to higher then normal.

If you want to know if the clutch, itself, works, unplug the solonoid. With no power to the solonoid, the fan should be on continuously. If it does not come on, you will want to look into it a bit farther.

I can't say for sure but many late model trucks (company spec'd) don't have a manual switch and I don't recommend covering the radiator on a later model truck for any length of time unless it's well below freezing. Are you concerned it's not working when needed? If it's above 85 and at idle or high-idle, and the a/c is on it should typically and noticeably be cycling in and out as called for by the a/c system.

it is normal for your fan to free wheel. if you locate your fuse panel, pull out the fuse labled fan. the fan should come on, & go off when fuse is back in place. you can put a toggle switch in place to manually turn fan on. I put one on my truck as soon as I got it. when the a/c is on the fan will kick off/on constantly. this will wear out the solenoid a lot sooner. I turn on the fan maually to keep the solenoid from kicking on/ off. the fan just stays on. I only do this when idle, for sleeping e.t.c.

This should be taught in every truck driving school. I personally thank you sir.

turn on your air conditioner and the fan will turn on shortly afterwards