It's not LOW on freon, it's empty. I would not recharge it until I found and repaired the leak. The best approach would be to pressurize it with dry nitrogen and 2 oz. of R22 then search for the leak with an electronic leak detector. Failing such facilities, charge it with R12 and dye, (since it is empty your dye is gone) find the leak with your UV lamp, recover the freon, fix the leak and recharge.

Any time a system is drawing into vacuum, see to it immediately before moisture is drawn into the system.

Your best bet would be to repair the leak, evacuate and charge by weight, not pressures. Failing equipment or means to accomplish this, low side will be around 30 and high around 250 or until sight glass is clear. This will depend on ambient temperature.

Good luck,