Hi, LastCJ7! For those who aren't aware, the York air conditioning compressors make a terrific air supply source for off-road vehicles. York A/C compressors were popular with Ford, AMC, I-H and others that wanted a rugged, high-output compressor unit.
Also unknown to many, including those building air supply systems for off-road use, is that the York compressor you describe has a "crankcase" and oil reserve for the crankshaft and bearings. When this crankcase runs dry, just like with an engine's crankcase, the compressor bearings and crankshaft, pistons and other parts, starve for lubrication and fail, often seizing.
The clutch you describe is a simple, magnetic field design. You can test the clutch engagement by magnetizing the clutch. There is one wire coming from the clutch unit, and if you apply 12-volt current here, you activate the magnet and lock up the clutch. Simple test is to run a fused jump lead to that wire. If the clutch locks, the magnet is good. These magnets do fail and should be available. Make sure you have a sufficient ground, although this is generally assured by the metal case attaching solidly to the engine. It is presumed that your grounds to the engine are good.
Test the magnet/clutch activation. When activated, you will see and hear the clutch engage. When engaged with the engine running, the load on your engine should be noticeable if the compressor has good seal. Clutch engagement causes the compressor's crankshaft to turn.
I've always wondered what is normal "oil consumption" for these compressors. Do you add much oil after the initial fill and leveling? I know the crankcase oil level should be checked periodically. I would guess that very little oil gets past the rings and into the air supply. If it does, do you filter the air to eliminate oil contamination when inflating tires and using compressed air? For air tool operation, this is a non-issue, as it's advantageous to oil your air tools regularly!
Kilby Enterprises does a lot of onboard air stuff with the 210 compressor. This is a high output unit, and in top form, it is capable of running air tools! One concern with the York units is mounting position, as the suction port must be on top. See the notes at the Kilby Enterprises site. Kilby also has parts if you need them, plus this York Manual in PDF download sections. For the clutch service section, click here for PDF service steps—thanks, Kilby Enterprises!
Let us know whether the clutch engages...If not, it's straightforward to replace the magnet—when you find a new or good used one. Kilby Enterprises does offer new service parts for these units.