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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.

  • Welcome to the site @Kading, you are right to not use refrigerant and dye, with that big a leak you'd lose it all and it's a powerful greenhouse gas. – GdD Jun 25 '18 at 13:43
  • The dye is designed to be soluble with the refrigerant lubricant oil so the system would need to be turned on (and you can't since the leak is too large). However, in most cases a dye tends to be already added when the system receives its first charge in the factory, and even if not, a huge puddle of refrigerant oil along the component surely can't be missed by naked eye. Begin by thoroughly examining the whole piping and circuit and checking for any evident huge oily spot, with both a normal and a blacklight torch. – Al_ Jun 25 '18 at 13:48
  • Thanks. I did trace the entire path of the system but I could not see any obvious sign of any leaks just by visual inspection. Point taken, though, about the dye already having been added in the factory. I'll purchase a UV flashlight and see if I can find it without having to recharge the system first. – Kading Jun 25 '18 at 13:52
  • My question still stands, though. What if I can't find the leak without having to recharge the system so it can run and circulate the dye. Is it safe to use alternate gases like nitrogen or CO2 to temporarily charge the system? Which gases are safe to use so as not to damage the system? – Kading Jun 25 '18 at 14:06
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    So I finally found the leak using. it was the O-ring on the high pressure side connection into the compressor. I changed the O-ring and after that I was able to pull a -30 psi vacuum and hold it for 30 minutes. Thank you everyone for your help. – Kading Jul 16 '18 at 18:01

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