I'd recommend calling a hvac contractor & get him to use his electronic leak detector. It looks something like this.
He's gonna charge you a service call & a fee for finding your leak. Sometimes they'll let that go towards the repair if its something like a evaporator. Just depends. If I were you I wouldnt even bother finding it, unless your planning on spending the money to have it fixed.
Life is like a jar of jalapenos. What you do today might burn your ass tomorrow.
Call a contractor, they will come out check electronically and with bubbles. They may need to boost the pressure in the system with nitrogen. And as hvachero indicated, if the leak is in a coil it likely will be unrepairable and the coil will have to be replaced.