If the clutch engages you will see the inner wheel on the compressor move with the outer wheel (the pulley). Usual cause is loss of refrigerant causing low pressure, and the low pressure switch signal means that A/C ECU won't let the compressor run.
IIRC early cars had the fuses and relays in the black box above the washer reservoir, on later cars the box was done away with (presumablt due to owner spilling washer fluid all over the black box) and the fuse/relays were scattered around the engine compartment (near the maxi fuses I think?)
You'll need to get a "vac and re-gas" (vacuum out all refrigerant first, test for leaks, then refill with refrigerant and compressor lubricant, plus usually a fluorescent green dye to make leak detection a little easier).
Any of the O rings can leak, the condenser at the front can split/leak, or any of the pipes can leak if anything keeps rubbing on them (even a P clamp that's supposed to stop them moving around) and the compressor can leak if the casing gets small cracks/splits. It can be a long journey to try and find the root cause of non-functioning A/C, of which there may be several, including a faulty A/C ECU or other electrical issues.
1996 Portofino 20vt & 2000 Pearl White Plus
1985½ & 2016 2017 Fiat 124 Spider + XF Sportbrake