Just some general info.
AC gas does diminish over time, it will never last forever.
Use it often to keep all the seals lubricated etc. Even just a couple of minutes. It doesnt have to be on cold to be working, it will still dehumidify the air on warm etc.
Dye is added to trace future leaks technically. As its illegal to knowingly vent R12, R134a, R1234yf etc to atmosphere. Nitrogen should be used for leak finding. The machine will remove gas, then vacuum the system and monitor the pressure. This is the basic leak check, but it can be wrong, as leaks are normally tiny, and often only found when system is running.
You can also get sniffers, which is what i prefer, they detect refrigerant particles.
Its worth making sure the place are doing an AC service, not just a regas. Ive known places to just suck any remaining gas out, and stick new gas in.
A proper service would keep vacuuming the system to make sure any residual moisture is removed, pressure test the vacuum for leaks, replace any oil removed (machine weighs what came out) regas with dye, then performance test it on the machine.
Thats where going somewhere reputable, like Honda comes in.
