The A/C system in my 2013 Subaru Impreza is not working. The system reads zero pressure on both HI and LO sides when I hooked up a gauge set to it indicating that it must be completely empty. I hooked up a 3 cfm 2-stage vacuum pump and ran it for about 15 minutes but the best it could do was around -27 psi and it would not hold the vacuum at all after I turned the pump off so there is definitely a sizable leak in there somewhere that I need to find and fix.
I'd like to go the flourescent dye / UV light method but I don't want to charge the system with refrigerant just to do this since I would then have to evacuate the refrigerant in order to repair the leak. I do not have a license to do that. It would also be a waste of refrigerant.
My question is: can I use other gases like nitrogen or CO2 to temporarily charge the system so I can use the dye/UV light? Is there any other method to find the leak that anyone can suggest?
Thanks so much in advance for any advice and suggestions.