Sorry for the inconsistent audio quailty...
My 1966 Mustang GT came to me with the AC inop. The receiver dryer was loose and needed replacing (they always do if exposed to the air for more than a few...minutes, hours?). After that I vacuum down the system to -27 inches and then charge it with R-12. The belt slap and subsequent compressor vibrations were a common customer complaint in the day, so Ford made an extra pulley dealers could install to eliminate the problem. In addition to the bad receiver dryer the thermostatic switch in the under dash blower needs replacing which is why the compressors magnetic clutch is jumped to the battery.
The R-12 can be had on eBay or Craigslist. I paid /can. The R-12 hose and value run on Amazon. The Ford Mineral oil was at NAPA. So to recharge it plus for the dryer and I'd call myself lucky to get any A/C recharged for that price! The gauges run 0 and the vacuum pump 0 but my local O'Reilys auto parts lets you rent (buy) then return them, so zero dollars there.
The non-adjustable pulley Ford made to stop the pulley slap is for a reproduction and the thermostatic switch another . So for a few more dollars I'll have it back in perfect working order!
Questions and comments welcome.