A/C not working on 89' ranger
I recently inherited a 1989 Ford Ranger XLT from my grandpa that recently passed away (old, but only 60K miles or so). The only issue with it (other than needing a new paint job) is that the A/C does not work. I first thought it needed some refrigerant (it was retrofitted for R-134a). I hooked up a gauge to the low pressure side and it's fully charged. I called up my uncle and he thinks it's the A/C clutch, he had me listen for the "click" sound of the clutch engaging which I did not hear. I did check the fuse for it and it's good. Any help would be appreciated.
I should note that I'm relatively new to doing work on vehicles and have no ideal what the A/C clutch looks like(my background is in IT, not fixing cars/truck so I'm a total noob.)