To find out how much R-12 your *specific* 1979 El Camino's AC system originally held, you'd need to consult a couple of sources:
* The owner's manual: If you have the original owner's manual, it might specify the refrigerant capacity.
* A Chevrolet parts catalog from 1979: These catalogs often included such specifications. You might find a digital version online through a classic car parts website or a library database.
* A reputable AC repair shop: They'll have access to resources that can likely identify the correct amount based on your vehicle's identification number (VIN).
Important Note: R-12 is no longer produced due to its ozone-depleting properties. If your El Camino's AC system needs refrigerant, it will need to be converted to use a modern, ozone-safe refrigerant like R-134a. This conversion requires specialized equipment and should be done by a qualified technician. Simply adding R-12 is illegal and environmentally irresponsible.