Automotive Air Conditioning Information Forum

A/C would blow cold for about 2–3 weeks, then slowly get warm. Took it to two different shops. Both used electronic sniffers, checked the usual spots, and couldn't find anything obvious. Both times they evacuated, recharged, added a bit of oil, and sent me on my way. The same thing happened again within a month.

The third shop suggested adding UV dye. I was skeptical at first because I'd heard the usual concerns — contamination, warranty issues, etc. But at that point I was tired of guessing. They injected the dye, told me to drive normally for a week with the A/C on, and come back.

Came back, they put on the UV light, and within a couple of minutes found a small fluorescent trail near the compressor shaft seal. Not a huge leak, but enough to lose refrigerant slowly over weeks. Replaced the seal, evacuated, recharged — been holding for a few months now.

What I took away: the electronic detector is still faster for a quick scan, and I wouldn't skip it. But for a slow, intermittent leak that only shows up over time, the dye made the invisible visible. No guessing, no throwing parts at it.

Have you had a similar slow leak that only dye could find? Or do you still stay away from it completely?

1. Assuming that you're not AI or a "bot", I'm surprised that a shop would just replace a compressor shaft seal instead of the entire compressor. Are you in USA?

2. As I stated before, some manufacturers do add UV dye to brand new vehicles. I use a combination of electronic sniffer, UV dye/light/goggles, soap bubbles, and visual examination for residue to find AC leaks.

The last leak I found and fixed was two leaking O-rings on my 1998 Frontier; I had replaced that high pressure line years ago and recently the O-rings leaked. You can see that the brand-new AC line needed shortening by 5.5mm at one end when compared to the factory one.