tracking down a leak

Ultraviolet dye is what we use. You can probably buy R134A with dye already in it or buy an injection kit. DO NOT put any foreign substances in your system. I have lost three AC machines in the last five years due to butane, stop leak and other crap. We make a customer sign a form now stating that there is nothing foreign in their system and a guarantee of repair to our machine if there is anything they don't know about.