Forget duracool, use red tek. At least sniffers can pick the stuff up.
If your system is empty then you have a leak, and when leak hunting sometimes a sniffer is your best friend. With red tek it is not that important to evacuate the air, rather, they recommend not doing it, but you should change your receiver/dryer to prevent any moisture problems. Pressures are comparable to R12 however the cooling is much better. This is the best alternative IMHO.
I don't know much about the early A/C systems, but if you have no power to the low pressure switch with the A/C switch on then my guess is that the A/C switch is no good. Far from an expert here though
