A/C dry nitrogen high-pressure decay test

2008 Prius definitely has a leak air-conditioning was working about a week and a half ago and today zero psi of refrigerant in the system.
1: performed a vacuum decay test passed with flying colors.
2: performed a high-pressure nitrogen decay test passed with flying colors
3: extremely sensitive heated diode electronica refrigerant leak detector test again past with not even the slightest whisper or beep to indicate there was a leak.
4: using ultraviolet trace or die installed in the system and using a very powerful bright UV light to help detect leak detection still a no-go absolutely clean. No leak detected

5: when you come across these situations that happen from time to time because leaks are not constant actually some of them turn on and off like a shut off or a blow off valve.
“ Question is what do you tell your customer after this ?.

 

i’ve came across this many times in the past 30+ years and actually got occasionally to see the leak up here right in front of my eyes instantly when there was no leak before and watch a leak turn off instantly and stop leaking.
In every scenario the leak was located on the high side of the component not at the bottom so the system was off at the time so all the oil and buy sink down and settle to the lowest part of the component.
Some leaks or pressure or temperature or vibration sensitive some leaks only happen when the temperature of the metal or the rubber or the combination of both are on the rising some leaks only happen when the temperature or the pressure are actually lowering. And there will be absolutely no oil stain no die no leak and then all of a sudden it pops open like a pop off valve a controlled solenoid valve releases the entire contents of the air-conditioning turns off you immediately perform a leak test right after that it holds vacuum and it holds pressure and it does not leak anymore no soap bubbles nothing you feel the system back up and repeat and it happens all over again right in front of you this I have witnessed several times very rare and it’s something my dad showed me and explain to me when I was 12.

As for the service fittings the valve cores on older vehicles I have a whole box kit and every time I get to a vehicle valve cores are one of the first things get replaced.
In one of my videos on my YouTube channel I actually show a valve core removal tool that you can change the valve cores that were leaking on a vehicle while the system is completely full charged and not lose any refrigerant.