Air Con Still Seemingly Leaking Despite Repairs. Any Help?

[callumhind]

Hi everyone. Apologies for the long post but I need to get the context across.

Back in May 2025, my A/C suffered a sudden loss of refrigerant, and came with a smell of the A/C insides and oil that was stronger when the car was first started up after a while, and the fans were blowing, which went away mostly after a few minutes. The first garage I took it to said it was the condenser that had failed, so I replaced it and had it re-gassed. Within a week the system had lost all cooling capability and I was back to square one.

I then took it to another garage recommended by a trusted family member who's into cars, who said it was the evaporator that had failed. They quoted me a very good price to replace it, so I had them do the work in late September/early October 2025.

The car had to go back to that garage twice in quick succession as the controls for the A/C system were all messed up, and needed putting back together properly. Despite these repairs, the system was still losing all of its refrigerant within a week. They used soapy water and bubbles formed at the expansion valve, and was told that it would need new o-rings.

Last week, my car was with my usual garage having some unrelated work done, and my dad arranged for them to swap these o-rings for me. They replaced the two that go from the pipes into the expansion valve, but not the two that are between the expansion valve and the evaporator, as they didn't know the evaporator had been replaced, and thought that it would be seized on. The result of this was that the system lost its cooling capability in around 4-6 weeks as opposed to the <1 week as before, which was a meaningful improvement.

This week I replaced both the expansion valve and the o-rings between the expansion valve. It turns out that the second garage had re-used the old o-rings and the one on the left had split, which to me explained the current leak. I took it for a re-gas today, it held a vacuum (which it always did), and it was recharged. Given that it had been leaking there before, I asked the garage to use an electronic sniffer to check for leaks, and nothing was detected. All positive signs so far.

I've just gotten home and used soapy water to test for peace of mind, and lo and behold, bubbles are still slowly forming. I'm at my wits end with this now as its been a 14 month saga, nearly every component has been replaced, and it still appears to be leaking. I'm going to wait until it probably dies again before contacting the third garage, but I was wondering if anyone has any ideas of what could still be leaking.

The new o-rings were from an OEM VW parts supplier. The expansion valve was aftermarket, and looks near-identical to the OEM one that I replaced.

Thanks for reading, and thanks in advance for any help anyone may be able to give.

[RUM4MO]

I hope that you "wetted" the new O-rings with a PAG oil or some other suitable lubricant before fitting them, if you didn't, there is a good possibility that one or both have gone damaged with re-assembling things.

[CarbonChaos]

I second that RUM4MO , fitting O rings in a tight area can be trying at best it just takes one miss aligned attempt to pinch/ nick them and your cooked. Also unless it’s a massive leak with most A/C machines the vacuum test is useless to pin point a broken o ring type leak.

On the positive side you have narrowed down the system and now know where it’s leaking from