That's the manual system then, first check all the fuses linked to the AC system including for the auxiliary electric cooling fan in front of the condensoer and radiator.
If everything looks ok and it's still not clicking the clutch in, identify the feed wire to the clutch on the compressor, get yourself a jumper wire and connect to it then tap the other end on the battery +ve terminal. If you hear it click, repeat the test with the engine running to make sure it doesn't make any horrible noises.
If so, chances are you'll get away with a recharge kit but make sure you have an R134a system and not and R12 before buying this kit or similar :
https://www.ebay.com.au/itm/284664407044
I haven't read the full listing so make sure the recharge gas canister also has some oil in it for the compressor etc and preferably a leak sealer too.
If none of that appeals or you have an R12 system, you'll probably need an AC specialist to convert the valves to R134a, vac the system down (consider renwing the reciever dryer too!) and check for leaks then recharge the system with gas and test before handing it back to you.
Good luck and let us know how you get on!
